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IB MYP Chemistry : Bonding – reaction kinetics Practice Question

IB myp 4-5 Chemistry – Practice Questions- All Topics

Topic :Bonding-Reaction Kinetics

Topic :Bonding- Weightage : 21 % 

All Questions for Topic :structure and bonding,properties,chemical formulas,chemical reactions and the conservation of mass; balancing,equations, the mole concept and chemical calculations;
reaction kinetics [rates, and factors affecting rates/collision theory],equilibria/reversible reactions,energy changes in reactions, endo- and exothermicity; combustion of fuels)

Question  (25 marks)

This investigation explores how cooking methods affect meat texture and examines innovative acid-based cooking techniques.

Experimental Context:

When eggs or meat are cooked, proteins undergo chemical changes. Different cooking methods produce different physical properties in cooked meat. Special equipment measures the force needed to break meat fibers (in newtons, N).

The student took two pieces of the same meat of identical size, one cooked and the other uncooked. They placed the meat samples in the equipment and measured the breaking force.
The results are shown below.

Question a (2 marks)

Topic: Evaluating Hypotheses

A student predicted: “If meat is cooked longer, the breaking force will be lower because heat breaks chemical bonds.” Experimental results showed:

Sample Breaking Force (N)
Uncooked meat 121
Cooked meat 315
▶️Answer/Explanation

Evaluation:

The hypothesis is incorrect because:

  • Cooked meat required higher breaking force (315N vs 121N)
  • Cooking causes protein coagulation, creating a firmer texture
  • Heat breaks weak bonds but forms new cross-links between proteins

Key Concept: Denaturation alters protein structure but increases mechanical strength through new bond formation.

Question b (2 marks)

Analyze the MY-P meat substitute cooked with different fruit juices (minimum 280N required):

Sample Juice Used pH Breaking Force (N) Suitable to Eat?
1 None – 130 □
2 Lime + Lemon 2.0 + 2.6 300 □
3 Orange 3.8 275 □
4 Lemon 2.6 290 □
5 Lime 2.0 320 □
▶️Answer/Explanation

Suitable Samples: 2 (Lime+Lemon), 4 (Lemon), and 5 (Lime)

Justification:

  • All exceeded 280N threshold
  • Lower pH juices (≤2.6) were more effective
  • Orange juice (pH 3.8) was insufficient
  • Control (no juice) showed minimal change

Chemical Principle: Acid denatures proteins similarly to heat but at lower temperatures.

Question c (1 mark)

State the purpose of Sample 1 (no juice):

▶️Answer/Explanation

Answer: Control experiment to show the natural state without acid treatment and provide baseline data for comparison.

Purpose: Demonstrates that texture changes require acidic conditions, not just time.

Question d (2 marks)

Outline one improvement to the method:

▶️Answer/Explanation

Improvement: Use standardized juice volumes/masses to control acid concentration variables.

Alternative: Measure pH of the meat-juice mixture during cooking to monitor reaction conditions.

Rationale: Ensures consistency in acid exposure across samples.

Question e (1 mark)

Suggest a research question about minimum effective pH:

▶️Answer/Explanation

Question: “What is the minimum pH required to achieve a breaking force of 280N in MY-P meat substitute?”

Focus: Establishes quantitative relationship between acidity and cooking effectiveness.

Question f (17 marks)

Design an investigation using HCl solutions (pH 2.6-3.8) to determine the minimum cooking pH for MY-P.

Required Components:

  1. Identify independent, dependent, and control variables
  2. List necessary equipment
  3. Describe step-by-step method
  4. Specify data collection procedures
  5. Include safety considerations
▶️Experimental Design

Variables:

  • Independent: pH of HCl solution (2.6, 2.8, 3.0, 3.2, 3.4, 3.6, 3.8)
  • Dependent: Breaking force (N)
  • Controls: MY-P sample size, immersion time (15min), temperature (25°C)

Equipment:

  • pH-adjusted HCl solutions
  • Force measurement device
  • Timer
  • Thermometer
  • Safety goggles and gloves

Method:

  1. Prepare HCl solutions at 0.2 pH intervals
  2. Immerse identical MY-P samples for 15 minutes
  3. Blot dry and measure breaking force
  4. Repeat each pH condition 3 times
  5. Plot breaking force vs. pH to determine threshold

Safety:

  • Use dilute acid solutions
  • Wear eye protection
  • Neutralize waste before disposal

Question:

Plot the volume of carbon dioxide gas evolved V(CO2) against time t. You can do this by hand or by using graphing software. Remember that a smooth curve is required to represent the relationship between the data points.

▶️Answer/Explanation

Ans:

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