two questions please help?!!?

Question

1. If 11.4mL of 0.100Molar MgCl2 is needed to completely react 15.0mL of AgNO3 solution, what is the molarity of the AgNO3 solution?
MgCl2 (aq)+2AgNO3(aq) ->2AgCl(s)+Mg(NO3)2(aq)

2. How many liters of H2 gas at STP are produced when Zn react with 250mL of 3.00M HCl?
Zn(s)= 2HCl(aq) -> ZnCl2(aq)=H2(g)

please help i also need to show work so if you can walk me through it that would be awsome!!! thanks so much

Answer 1

Find the total no of moles of each substance in the reaction. To find the no of moles from the molar concentration and the volume, multiply the concentration (0.1M for the MgCl2) times the volume in liters (11.4mL = 0.0114L). So for the MgCl2 you are supplying a total of 0.00114 moles. Your reaction equation tells you that each mole of MgCl2 will react with 2 moles of AgNO3; that means that the AgNO3 solution contained exactly twice the no of moles in the MgCl2 solution, so the total no of moles of AgNO3 reacted is 2*0.00114 = 0.00228. This no of moles was in 15.0mL of solution, so the molar concentration( moles per liter) is 0.00228/0.015 = 0.152M

In part 2, each mole of Zn reacted will produce 1 mole of H2; each mole of Zn will react with 2 mole of HCl. As above, get total moles of HCl by multiplying molar concentration times volume (L), or 3*0.25; the no of moles of Zn is half this, so the moles of H2 produced is .5*3*.25. To get the gas volume, use the perfect gas law PV=nRT, where n = no of moles, and R = universal gas constant = 8.3145 J/(mole ºK).

Answer 2

Moles MgCl2 = 0.1(11.4)/1000=0.00114

MgCl2 >> Mg2+ + 2Cl-

Moles Cl- = 2(0.00114)=0.00228 = moles Ag+

15 mL = 0.015 L

M ( AgNO3)=0.152


Moles HCl = 3.00 ( 250)/1000 = 0.00200

Zn +2 HCl >> ZnCl2 + H2

the ratio between HCl and H2 is 2 : 1 so we get 0.00100 moles H2

pV = nRT

V = nRT /p = 0.00100 ( 0.08206) 273 /1 = 0.0224 L

Answer 3

For me gp4rts has answered right! Good job!