Chemistry

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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  1. I don't see anything MAJOR that's wrong but I think you're a litte sloppy. I hope that's sloppy with typing and not the chemistry. I see decimal points missing, I would have used 65.4 for Zn instead of 65 and on the 0.22 mols I would have carried the numbers out further since that number of significant figures is allowed. Some of the other answers could have allowed more numbers to be used but you rounded off too early.

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