# IB MYP 4-5 Chemistry chapter 12 : Transfer– Practice Questions

### Question:

Calculate the amount (in moles) in each of the following masses:
a) 4.00 g of sodium hydroxide NaOH (Mr = 40.00 g mol−1)
b) 58.80 g of sulfuric acid H2SO4 (Mr = 98.09 g mol−1)
c) 14.6 g of hydrogen chloride HCl (calculate Mr)*
d) 58.8 g of nitric acid HNO3 (calculate Mr).*
*Use the values of Ar on the periodic table.

Ans: a) moles = mass (g) / molar mass (g mol1)
= 4.00 / 40.00 = 0.100 mol

b)
58.80 / 98.09 = 0.5994 mol
c)
14.6 / 36.5 = 0.400 mol
d)
58.8 / 63.02 = 0.933 mol

### Question:

Calculate the concentration, in mol dm−3, of the following:
a) 0.20 mol of nitric acid, HNO3, dissolved in water to make a 0.50 dm3 solution
b) 8.00 g of sodium hydroxide, NaOH, dissolved in water to make a 0.80 dm3 solution
c) 0.45 mol of sulfuric acid, H2SO4, dissolved in water to make a 0.75 dm3 solution
d) 6.80 g of ammonia, NH3, dissolved in water to make an 800 cm3 solution.

Ans: a) 0.20 / 0.50 = 0.40 mol dm3
b)
moles = 8.00 / 40.00 = 0.200 mol
0.200 / 0.80 = 0.25 mol dm–3

c)
0.45 / 0.75 = 0.60 mol dm–3
d)
moles = 6.80 / 17.04 = 0.400 mol
0.400 / 0.800 = 0.499 mol dm–3

### Question:

Two students are each asked to measure out three 9.5 g samples of a reactant. When their teacher checked their results, she found the following: Comment on the level of accuracy and precision of both sets of data.

Ans: Student A results are not accurate as they are all different from the actual value of 9.5 g. The results are not precise as they are all different from each other. Student B results are not accurate as they are not close to the value of 9.5 g. However, they are precise as the three results are similar to each other.

### Question:

The difference between precision and accuracy is important in the chemical laboratory. When you collect data, which of the following situations is easier to explain and why: results with poor precision or results with poor accuracy?

Ans: Results with high precision but low accuracy are often associated with equipment that has not been correctly calibrated. For example, an electronic balance that does not initially read 0.00 g or a pH meter that has not be calibrated with buffer solutions.

### Question:

a) Copy the table below and complete the missing data. Ans: b) Which piece of apparatus listed in the table is the most accurate?

Ans: The volumetric flask as it has the lowest percent uncertainty.

### Question:

What are the advantages and disadvantages of laboratory apparatus with fixed volumes?

Ans: The advantage is that with the correct positioning of the meniscus, an accurate volume can be achieved. The disadvantage is that for a school laboratory, fixed volume apparatus are not flexible and require the purchasing of a lot of equipment to suit all practical needs.

### Question:

Suggest reasons why measuring a volume of a liquid with a measuring cylinder is not good laboratory technique.

Ans: Measuring cylinders are relatively inaccurate as they have a high percent uncertainty. A burette or graduated pipette are more accurate apparatus for variable volumes of liquids.

### Question:

Convert each of the following measurements into scientific notation and state the number of significant figures.
a) 0.00045 mg
b) 1545 kg
c) 32.65 cm
d) 12.056 pH units.

Ans: a) 4.5 × 104 (2 sf)
b)
1.545 × 103 (4 sf)
c)
3.265 × 101 (4 sf)
d)
1.2056 × 101 (5 sf)

### Question:

To how many significant figures should the answer of each of the following calculations be expressed?
a) 3.864 × 52

Ans: 3.864 × 52 = 200.928 = 2.0 × 102 (2 sf)
The least accurate measurement is 52 with 2 significant figures.

b) 3.24587 ÷ 13.5

Ans: 3.24587 / 13.5 = 0.240 (3 sf)

### Question:

Describe the color change at the point of neutralization of the ethanoic acid by sodium hydroxide.

Ans: At the point of neutralization, colour change is from colorless to pink.

### Question:

Write the balanced chemical equation for the reaction between ethanoic acid and sodium hydroxide.

Ans: CH3COOH(aq)+ NaOH(aq) → CH3COONa(aq) + H2O(l)

### Question:

Calculate the average volume (in dm3) of sodium hydroxide released from the burette.

Ans: The answers to these questions are dependent on the concentration of the ethanoic acid provided to the students.

### Question:

Calculate the number of moles of sodium hydroxide in this volume.

Ans: The answers to these questions are dependent on the concentration of the ethanoic acid provided to the students.

### Question:

Using the balanced chemical equation, calculate the concentration (in mol dm−3) of the ethanoic acid solution.

Ans: The answers to these questions are dependent on the concentration of the ethanoic acid provided to the students.

### Question:

Compare this concentration with the actual concentration of ethanoic acid (your teacher will know this).

Ans: The answers to these questions are dependent on the concentration of the ethanoic acid provided to the students.

### Question:

Comment on the accuracy of your result and your level of precision in using this analytical technique.

Ans: The answers to these questions are dependent on the concentration of the ethanoic acid provided to the students.

### Question:

Comment on what the starting point of the pH curve on the y-axis tells us about the strength of hydrochloric acid?

Ans: The initial pH is 1.0 unit. This tells us that the acid is a strong acid.

### Question:

Interpret the pH curve and explain why the pH of the solution starts to increase as sodium hydroxide is transferred from the burette to the conical flask.

Ans: The addition of sodium hydroxide will start the neutralization reaction. As the acid present in the flask is neutralized, the pH will start to rise as the solution becomes less acidic and more alkaline.

### Question:

After 25 cm3 of sodium hydroxide has been transferred to the reaction mixture, there is a sudden increase in the pH level. What does this tell you about the amount of hydrochloric acid that remains unreacted in the conical flask? Justify your answer with scientific reasoning.

Ans: After 25 cm3 of sodium hydroxide has been transferred to the flask, no more hydrochloric acid will be present. This results in a sudden increase in the pH of the reaction mixture as the solution is now alkaline in nature.

### Question:

State the name of the carboxylic acid formed when heptanol is oxidized.

Ans: heptanoic acid

### Question:

Name the ester which is produced from each of the following pairs of reactants:

a) propanol and butanoic acid

Ans: propyl butanoate

b) methanol and ethanoic acid

Ans: methyl ethanoate

c) hexanol and pentanoic acid

Ans: hexyl pentanoate

d) butanol and methanoic acid.

Ans: butyl methanoate

### Question:

Write the word equation for the reaction between methanol and ethanoic acid.

Ans: Methanol + ethanoic acid → methyl ethanoate + water

### Question:

Deduce and record the name for each of the esters formed in your reactions.

Ans: Methyl ethanoate; ethyl ethanoate; propyl ethanoate; butyl ethanoate, methyl propanoate; ethyl propanoate; propyl propanoate; butyl propanoate; methyl benzoate; ethyl benzoate; propyl benzoate; butyl benzoate.

### Question:

Explain the purpose of the concentrated sulfuric acid in the esterification reaction.

Ans: Concentrated sulfuric acid acts as a catalyst to maximize the yield of the ester.

### Summative assessment

Analytical chemistry
Titration is a quantitative analytical technique that has been used by chemists in one form or another for over 150 years. Advances in technology have made data probes such as a pH probe reliable and more cost effective, and they are now commonly used in school laboratories. They can be used to track a change in pH over the course of a titration. Alternatively, indicators can be used to track pH changes visually. The diagram shows the color changes of different acid–base indicators in acidic and alkaline environments. ### Question:

State the pH at which methyl red indicator changes color.

Ans: pH = 46

### Question:

List the indicators that have more than one distinct color change.

Ans: Thymol blue; methyl yellow; bromothymol blue; methyl orange.

### Question:

Comment on the differences between phenolphthalein and bromothymol blue in terms of color changes. Identify and justify which indicator has a narrow pH range for the change in color.

Examine the pH curves of two different acid–base titrations. Ans: Phenolphthalein has one distinct colour change from colorless (acidic) to pink (alkaline); the colour change occurs over a narrow pH range of 1 unit; bromothymol blue has a gradual change from yellow to green to blue; the colour change occurs over a broad range of pH 6.5 to 8.0.

### Question:

For the titration of a strong acid with a strong base, the equivalence point at which base completely neutralizes the acid has a pH of 7.0. Select and justify your choice of an indicator that will allow you to visually determine the equivalence point.

Ans: Indicator with a narrow pH range of 6.0 to 8.0 is required; phenol red is ideal for this titration.

### Question:

Discuss why bromophenol blue would not be a good choice of indicator for the titration of a strong acid and a strong base.

Ans: The pH range for the colour change is too low; at pH 4.05.5.

### Question:

For the titration of a weak base with a strong acid, determine the initial color of solution if the indicator methyl yellow is used. State the color at the completion of the titration.

Ans: Yellow; pink.

### Question:

Select and justify your choice of an indicator that will allow you to visually determine the equivalence point in the weak base– strong acid titration.

Ans: The pH of the equivalence point is approximately 5.50; methyl red.

Investigating the transfer of hydrogen ions within an aqueous solution
We know from our work in Chapter 3, Consequences, that a strong acid will completely dissociate in solution into its ions, and a weak acid will undergo partial dissociation into its ions. The pH of a solution is a measure of the concentration of hydrogen ions, H+, present in a solution. You are provided with the following materials:
0.10 mol dm−3 solution of ethanoic acid and hydrochloric acid
0.010 mol dm−3 solution of ethanoic acid and hydrochloric acid
0.0010moldm−3 solution of ethanoic acid and hydrochloric acid
0.00010moldm−3 solution of ethanoic acid and hydrochloric acid
pH probes

### Question:

Choose a hypothesis to investigate from the list below. Explain your choice with scientific reasoning.

a) A decrease in the concentration of an acid will increase the pH of the solution.

b) The degree of dissociation of an acid is dependent on the initial concentration of a weak acid.

c) There is no difference in the pH of a solution of a strong or weak acid, when the initial concentration is identical.

Ans: Choice of hypothesis is supported by scientific reasoning and at least four different points are made.

### Question:

the independent and dependent variables, and other variables being controlled
how you will collect quantitative and qualitative observations in your investigation.

Ans: Independent; and dependent variables are selected; control variables are listed; possible qualitative observations are discussed and the method of recording is outlined; quantitative raw data that could support the hypothesis is identified and the method of presentation of this data is outlined.

Analysis and evaluation
A student performed an acid–base titration in the school laboratory and collected quantitative data. The reaction was between a 0.10 mol dm−3 solution of sodium hydroxide NaOH, a strong base, and 25 cm3 of a weak acid of unknown concentration and composition. We can give this acid the general formula HA.

### Question:

Write the chemical equation for the neutralization reaction between sodium hydroxide and the weak base HA.

Using a pH probe, the following data was collected and tabulated. Ans: NaOH(aq) + HA(aq) → NaA(aq) + H2O(l)
M1 Correct formula for reactants; M2 correct formula for products; M3 correct state symbol for all species. [Note: the question should read “…weak acid HA”, not “…weak base HA”.]

### Question:

Identify and explain which data was not correctly recorded.

Ans: pH 3.7 (2 sf not 3) / pH 4.330 (4 sf not 3) / pH 10.5 (3 sf not 4)
Any 2 of these for a maximum of 2 marks.

### Question:

Analyze the graph and comment on how you think the accuracy of the data collected would or would not affect the shape of the curve.

Ans: The general shape of the curve is the same as that of a typical weak acidstrong base titration curve; small variations in the slope of the tangents along the curve may be altered; overall the accuracy of the data will not affect the shape of the curve.

### Question:

Display the data in a graph of pH versus volume of sodium hydroxide added. Connect the data points with a smooth curve.

Ans: Axes correctly labelled; data points accurately plotted (2); smooth curve drawn.

The point of neutralization for this reaction occurs when the number of moles of acid equals the number of moles of alkali. At this point, there will be a rapid change in the pH of the solution.

### Question:

From your graph, estimate the volume of sodium hydroxide added to reach the point of neutralization.

Ans: 18.20 cm3

### Question:

Calculate the number of moles of sodium hydroxide at the point of neutralization.

Ans: Concentration (mol dm3) = amount of solute (mol) / volume of solution (dm3)
Amount of solute = concentration × volume of solution

= 0.10 × 18.2/1000;

= 0.00182 or 1.82 × 103 mol.

### Question:

Calculate the concentration (mol dm-3) of the weak acid.

Ans: Mole ratio of HA: NaOH is 1:1;
Concentration (mol dm3) = amount of solute (mol) / volume of solution (dm3)

= 1.82 × 103 / (25.0 / 1000)

= 0.0728 or 7.28 × 102 mol dm3 ;

Researching the chemistry of flavors

### Question:

From the article, identify the information required by chemists to synthetically reproduce natural flavors.

Ans: To synthetically reproduce natural flavors, chemists must identify the chemical profile of the particular food, this is the “unique combination of chemicals found naturally within” the food; the human mouth, nose and brain all play a role in processing the information relayed by receptors taste, texture and aroma are all detected and processed to identify the food; chemists must be able to synthetically reproduce these flavors.

### Question:

Explain why the role of chemists in the food manufacturing industry is becoming increasingly important.