Quantitative - Concentration

Question 1

What is concentration

Answer 1

The amount of substance in a certain volume

Question 2

Equation for concentration

Answer 2

Mass/volume (g/dm^3)

Question 3

How do you calculate the uncertainty of a set if results

Answer 3

Divide the range by 2

Question 4

How do you convert cm^3 into dm^3

Answer 4

÷ 1000

Question 5

What’s the concentration In mol/dm^3 of a solution containing 3.7g of calcium hydroxide ca(OH)2 in 0.25dm^3

Answer 5

You need to find the nummber if moles in calcium hydroxide

So find the relative formula mass = 74

Moles = mass ÷ Mr

3. 7÷74 = 0.050
4. 05÷ 0.25 = 0.2mol/dm^3

Question 6

How would you convert from a concentration in g/sm^3 to a concentration in mol/dm^3

Answer 6

Divide it by the relative formula mass

Question 7

25cm of 0.1mol/dm of sodium hydroxide is neutralized by 30cm of sulphuric acid

Work out the concentration of the sulphuric acid

Answer 7

Work out how many moles of sodium hydroxide you have
25cm = 0.025dm moles= concentration × volume
0.1 x 0.025 = 0.0025 moles

For every 2 moles of sulphuric acid there is one mole of sodium hydroxide so there must be 0.00125moles of sulphuric acid

There is 30cm of sulphuric acid which converts to 0.03dm

Concentration = moles ÷ volume

0.00125 ÷ 0.03 = 0.0417mol/dm^3