Key Calculations quiz

1. State the expression for calculating % yield.

% yield = (theroretical amount of products/actual amount of products)

% yield = (theroretical amount of products/actual amount of products) x 100

% yield = (actual amount of products/theoretical amount of products) x 100

% yield = (actual amount of products/theoretical amount of products)

Question 1 of 17

2. State the expression for calculating molar concentration

Molar concentration = Amount (in moles) x volume (in cm³)

Molar concentration = Amount (in moles)/volume (in dm³)

Molar concentration = volume (in dm³) / Amount (in moles)

Molar concentration = Amount (in moles)/volume (in cm³)

Question 2 of 17

3. Use Q=mcΔT and c=4.18J/°C/g. 25cm³ of sulfuric acid is put into a boiling tube. The starting temperature is 21°C. A spatula of iron filings is added. After a while the temperature reaches 33°C. What is the total heat energy change?

2153 J

3383 J

1254 J

2.153 kJ

Question 3 of 17

4. An oxide of nitrogen contains 26% nitrogen and 74% oxygen and has a relative molecular mass of 108. Find the empirical and molecular formulae for the oxide.

Empirical formula is N₂O₅. Molecular formula is N₄O₁₀

Empirical formula is N₄O₁₀. Molecular formula is N₂O₅

Empirical formula is N₂O₅. Molecular formula is also N₂O₅

Empirical formula is NO₂.₅ Molecular formula is N₂O₅

Question 4 of 17

5. A sample of hydrogen chloride gas has a volume of 48 dm³. What amount of hydrogen chloride is this?

2 moles

1 mole

48 moles

24 moles

Question 5 of 17

6. A graph shows the solubility of sodium chloride in water at 50°C is 34g/100g. At that temperature, what mass of sodium chloride will dissolve in 50g water?

17g

0.17g

0.68g

68g

Question 6 of 17

7. State the units of molar enthalpy change.

kJ/⁰C

J/⁰C/mol

mol/⁰C

kJ/mol

Question 7 of 17

8. A sample of bromine contained the two isotopes in the following proportions: bromine-79 = 50.7% and bromine-81 = 49.3%. Calculate the relative atomic mass of bromine

(81x79)/100 = 63.99

((79x50.7)+(81x49.3))/100 = 79.99

((81x50.7)+(79x49.3))/100 = 80.01

(81 + 79)/2 = 80

Question 8 of 17

9. Describe how to carry out an acid-alkali titration

1) Pipette 25cm³ of alkali into a conical flask. 2) Add indicator. 3) Fill a burette with acid, record the initial volume. 4) Whilst swirling the flask, add the acid dropwise until the indicator changes colour. 5) Record the volume and calculate the volume of acid which was added. 6) Repeat until two concordant results (within 0.2cm³ of each other). 7) Result is the average of all concordant results.

1) Pipette 25cm³ of alkali into a conical flask. 2) Add indicator. 3) Fill a burette with acid, record the initial volume. 4) Whilst swirling the flask, add the acid dropwise until the indicator is just about to change colour. 5) Record the volume and calculate the volume of acid which was added. 6) Repeat until two concordant results (within 0.2cm³ of each other). 7) Result is the average of all concordant results.

1) Pipette 25cm³ of alkali into a conical flask. 2) Add indicator. 3) Fill a burette with acid, record the initial volume. 4) Whilst swirling the flask, add the acid dropwise until the indicator is just about to change colour. 5) Record the volume and calculate the volume of acid which was added. 6) Repeat until three concordant results (within 0.2cm³ of each other). 7) Result is the average of all concordant results.

1) Pipette 25cm³ of alkali into a conical flask. 2) Add indicator. 3) Fill a burette with acid, record the initial volume. 4) Whilst swirling the flask, add the acid dropwise until the indicator changes colour. 5) Record the volume and calculate the volume of acid which was added. 6) Repeat until three concordant results (within 0.2cm³ of each other). 7) Result is the average of all concordant results.

Question 9 of 17

10. Calculate the relative formula mass(Mr) of aluminium nitrate (Al(NO₃)₃)

89

117

213

185

Question 10 of 17

11. What are the units for amount in Chemistry?

mol/dm³

Grams

Moles

g per 100g of solvent

Question 11 of 17

12. What is the empirical formula of a compound in which 0.48 g of carbon combines with 0.08 g of hydrogen and 0.64 g of oxygen?

CH₂O

C₂H₄O₂

C₄H₂O

CH₄O

Question 12 of 17

13. What mass of carbon dioxide is produced when 24g of carbon undergoes completely combustion?

176 g

88g

24 g

44 g

Question 13 of 17

14. What is meant by the term empirical formula?

A chemical formula that shows the actual numbers of the different types of atoms in a molecule

A method of calculating the ratios of masses in an equation

Baby food for emperors

A chemical formula that shows the simplest ratio of the numbers of atoms in a compound

Question 14 of 17

15. To determine the formula of a metal oxide by combustion, magnesium is heated in a crucible. Why is a lid used?

To stop carbon dioxide escaping

To stop the escape of magnesium oxide smoke

To keep the magnesium warm

To stop the escape of magnesium

Question 15 of 17

16. Complete the following expression: amount (in moles) =

Aᵣ / Mᵣ

Mᵣ / mass

mass / Mᵣ

amount (in moles) x Mᵣ

Question 16 of 17

17. In a chemical reaction, 250 kJ/mol is taken to break all the bonds and 280 kJ/mol is released when new bonds are formed. What is the overall molar enthalpy of the reaction?

-30 kJ/mol

+30 kJ/mol

-530 kJ/mol

+530 kJ/mol

Question 17 of 17

Key Calculations quiz

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