 # Stoichiometry Questions and Answers (Page 3)

## Stoichiometry questions and answers (Page 3)

### Question 1

Copper reacts with concentrated nitric acid as shown by the equation below:

Cu(s) + 4HNO3(aq) → Cu(NO3)2(aq) + 2NO2(g) + 2H2O(l)

1. Suggest one observation made when copper reacts with concentrated nitric acid.
2. (i) Suggest the name of the salt of formula Cu(NO3)2.(ii) Using the equation, determine whether copper is oxidised or reduced when it reacts with concentrated nitric acid.
3. An excess of copper is added to 25.0cm3 of 16.0 mol/dm3 HNO3. Using this information, together with the equation above, calculate the volume of NO2 formed at room temperature and pressure.
4. When heated, Cu(NO3)2 decomposes to form CuO, NO2 and O2. Construct the equation for this reaction.
5. To a sample of Cu(NO3)2(aq), a student adds aqueous ammonia drop by drop until it is in
excess.(i) Describe what is observed.

(ii) The student repeats the experiment but adds aqueous sodium hydroxide instead of
aqueous ammonia. Describe what is observed.

### Question 2

1. Silver nitrate can be prepared by reacting silver oxide with dilute nitric acid. Ag2O + 2HNO3 → 2AgNO3 + H2O

Excess silver oxide is reacted with 30.0 cm3 of 0.150 mol/dm3 nitric acid. After purification the percentage yield of silver nitrate is 80.0%. Calculate the mass of silver nitrate prepared, giving your answer to three significant figures. [Mr of AgNO3 = 170]

2. Phosphorus can be manufactured from calcium phosphate, Ca3(PO4)2 as follows: 2Ca3(PO4)2 + 6SiO2 + 10C → 6CaSiO3 + 10CO + P4

What is the maximum mass of phosphorus that can be made using 300g of silicon dioxide, SiO2?

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