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UCE (O-Level) Quantitative aspects of chemical change — practice questions

Explore 4 free Quantitative aspects of chemical change questions in UCE (O-Level) Chemistry. Open each question or exercise to read its content, reference answers and available explanation.

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Quantitative aspects of chemical change questions and exercises with answers

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What name is given to the reagent that is completely used up during a chemical reaction?Read the answer and worked solution →Which technique is used to determine the concentration of an unknown solution?Read the answer and worked solution →Percent yield compares the actual yield of a reaction with which other quantity?Read the answer and worked solution →What is the number written in front of a substance in a balanced chemical equation called?Read the answer and worked solution →

Worked practice questions

What name is given to the reagent that is completely used up during a chemical reaction?

  1. The excess reagent
  2. The standard reagent
  3. The neutral reagent
  4. The limiting reagent
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Correct answer: D. The limiting reagent

1. When substances are mixed, one of them usually runs out before the others do. 2. A reagent that is completely used up in the reaction is the limiting reagent. 3. Once it is gone the reaction stops, however much of the other substances remains. 4. The reagent that is not completely used up is called the excess reagent. _Source: Siyavula Physical Sciences Grade 11 (Everything Science, CC BY 4.0), Chapter 8: Quantitative aspects of chemical change_

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Which technique is used to determine the concentration of an unknown solution?

  1. A titration
  2. A filtration
  3. A distillation
  4. A separation
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Correct answer: A. A titration

1. A titration is a technique for determining the concentration of an unknown solution. 2. The unknown solution is titrated against a standard solution of known concentration. 3. Acid-base reactions and redox reactions are both commonly used for titrations. 4. Filtration separates a solid from a liquid and tells you nothing about concentration. _Source: Siyavula Physical Sciences Grade 11 (Everything Science, CC BY 4.0), Chapter 8: Quantitative aspects of chemical change_

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Percent yield compares the actual yield of a reaction with which other quantity?

  1. The measured mass
  2. The theoretical yield
  3. The starting volume
  4. The excess reagent
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Correct answer: B. The theoretical yield

1. The actual yield is the amount of product produced when the reaction is actually carried out. 2. The theoretical yield is the amount calculated for the reaction using stoichiometric methods. 3. Percent yield compares the actual yield with the theoretical yield. 4. The theoretical yield is the best the reaction could possibly do. 5. Real reactions lose product to spills, side reactions and incomplete conversion, so the actual yield is usually smaller. 6. Percent purity is a different measure and answers a different question, so it must not be confused with this one. _Source: Siyavula Physical Sciences Grade 11 (Everything Science, CC BY 4.0), Chapter 8: Quantitative aspects of chemical change_

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