# Stoichiometric Relationships Quiz

## Make sure to try these on a piece of paper first

Question #1-1 Paper 1 Difficulty: Easy

Identify which combination of processes would involve only an exothermic change.

A. Melting and Boiling
B. Melting and Freezing
C. Deposition and Freezing
D. Sublimation and Deposition

Question #1-2 Paper 1 Difficulty: Easy

Identify which of the following mixtures could be classified as strictly homogenous.

I. A metal alloy
II. Salt water
III. Oil and water

A. I and II only
B. I and III only
C. II and III only
D. I, II and III.

Question #1-3 Paper 1 Difficulty: Medium

What is the sum of the coefficients of this chemical equation when it is balanced using the smallest whole numbers?
${ C }_{ 4 }{ H }_{ 10 }\quad +{ \quad O }_{ 2 }\rightarrow { \quad CO }_{ 2 }+{ \quad H }_{ 2 }O$

A. 16
B. 33
C. 16.5
D. 37

Question #1-4 Paper 2 Difficulty: Medium

Carbonic acid ${H}_2{C}{O}_3$ is the weak acid which forms when ${C}{O}_2 (g)$ from the atmosphere dissolves in the oceans and then reacts with the water in it. The levels of carbonic acid in the oceans are being constantly monitored as evidence of damage to coral reefs and shelly organisms continues to rise.

(a) A student in a school lab wanted to simulate ocean acidification on a small scale. They reacted hydrochloric acid with calcium carbonate chips according to the balanced equation below:
$2{H}{Cl}(aq) + {Ca}{C}{O}_3(s)\rightarrow{C}{O}_2(g)+{H}_2{O}(l)+{Ca}{Cl}_2(aq)$

If the student used $40cm^3$ of $2.5mol.dm^{-3}$ HCl and 5.67g of ${Ca}{C}{O}_3$, determine which was the limiting reagent and thus how much ${C}{O}_2(g)$ that could be theoretically produced in this reaction.

(b) Once the ${C}{O}_2(g)$ was bubbled over into a beaker of water, it reacted with the water in the beaker and produced carbonic acid according to the equilibrium below: ${C}{O}_2(g) + {H}_2{O}(l)\leftrightarrow {H}_2{C}{O}_3(aq)$

Write the equilibrium equation for carbonic acid reacting with water and identify the conjugate acid and the conjugate base.

(c) In order to determine the actual concentration of ${H}_2{C}{O}_3$ which was produced in the beaker, the student carried out an acid-base titration.

The student used $0.2mol.dm^{-3}$ NaOH(aq) to titrate against $20cm^3$ of the acidic water and obtained the following results:

(i) Calculate the average titre to the correct number of significant figures and include the overall uncertainty of this calculation.
(ii) Write the balanced equation for the reaction which occurs between the NaOH and the ${H}_2{C}{O}_3$ in this titration and then determine the concentration of the ${H}_2{C}{O}_3$ which was in the sample of water.

(d) Studies have shown that in cooler parts of the ocean, for example near the north pole, the pH of the oceans is lower than in warmer regions. Suggest why temperature could affect the pH of the oceans.

Question #1-5 Paper 1 Difficulty: Medium

Which of the following statements are true when relating to the ideal gas equation below:
PV= nRT

I. Pressure is inversely proportional to volume
II. Volume is inversely proportional to temperature
III. A gas behaves most like an ideal gas at high temperature and low pressure

A. I and II only
A. I and II only
B. I and III only
C. II and III only