Amount of Substance

Question 1

finish the equations:
- metal hydrogencarbonate + acid —>
- ammonia + acid —>
- metal carbonate (+heat) —>

Answer 1

—> metal salt +water + carbon dioxide
—> ammonium salt
—> metal oxide + carbon dioxide

Question 2

Identifying the number of significant figures when…
- calculating involving multiplication and division.
- calculating involving addition and subtraction ONLY.

Answer 2

• final answer should be given to the same number of significant figures as the least number of significant figures in the data uses.
• number of significant figures is irrelevant, place value is more important.

Question 3

Define percentage yield and atom economy. give both equations.

Answer 3

percentage yield = compares the amount of product produced with the theoretical amount produced.
% yield = (actual yield / theoretical yield) x100

atom economy = proportion of the mass of atoms in the reaction which end up in the desired/wanted product.
atom ec = (mass of wanted product from equation / mass of all products from equation) x100

Question 4

What is the ideal gas equation? (+units)

Answer 4

PV =nRT

P = pressure (Pa)
V = volume (m^3)
n = number of moles
R = gas constant (8.31 J/molK)
T = temperature (K)

Question 5

What are the theoretical ideal gas behaviours, and the realities?

Answer 5

• Perfect elastic collision ——— energy is lost through friction.
• Random movements ——— diffusion isn’t random.
• No forces between particles ——— weak forces present.
• Negligible size ———gas particles do have some mass.

Question 6

Give two equations for calculating moles.

Answer 6

Moles = mass / Mr

Moles = concentration x volume
(conc (mol dm-3) , vol (dm-3) )

Question 7

How would you calculate the number of moles of a beginning base you are given, using a back titration. (simple)

Answer 7

1 - Add base to excess acid in a volumetric flask.
2 - Transfer sample of base+acid solution to conical flask and titrate using a different base.
3 - Calculate the moles of the different base used, and use to calculate moles of excess acid in sample.
4 - Multiply up to full volume of base+acid solution.
5 - Subtract from number of moles of acid added to volumetric flask.
6 - use to calculate number of moles of beginning base.