2 KOH(l) + H3PO4(l) --> K2HPO4(l) + 2 H2O(l)
a) How many mL of 0.450M KOH is needed to react with 60.0mL of 0.250M H3PO4?
a) 0.060L x 0.250M = 0.015 mol H3PO4
0.015mol H3PO4 x 2mol KOH / 1mol H3PO4 = 0.03 mol KOH
0.03 mol KOH x 1L/0.450 mol = 0.06667L = 66.67mL
b) How many mL of H2O is produced? (** Don’t forget to convert mL to L and back**)
0.03 mol H2O x (18 g/mol) = 0.54 g H2O x 1 mL / 1 g = 0.54 mL H2O.
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6. Zn(s) + 2HCl(l) ZnCl2(s) + H2(g) at STP
What mass of zinc is needed to produce 115 mL of hydrogen?
- it's given 115 mL of hydrogen, so can convert to 115/1000/22,4 = 0.0051 moles H2
- the ratio between HCl and H2 is 2 : 1, so the moles of HCl needed for this reaction is 0.01
- the ratio between Zn and H2 is 1 : 1, so the moles of Zn needed for this reaction is 0.0051
so the mass of Zn need is 0.0051*65 = 0.3315 (g)
How many moles of HCl are needed for the reaction? (2 marks)
b) 2 x 00051 = 0.01 mols
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N2(g) + 3H2(g) 2NH3(g) at STP
How many litres of ammonia gas is produced using 5 litres of H2?
N2 + 3H2 ---> 2NH3
- the ratio between H2 and NH3 is 3 : 2
- it's given 5 litres of H2, so the volume of NH3 formed is 5/3*2 = 10/3 = 3.33 (L)
How many moles of N2 are needed?
- 5 litres of H2 converts to 0.22 moles of H2
- the ratio between N2 and H2 is 1 : 3, so the moles of N2 needed is 0.074 mol
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