The reaction of 0.779 g K with O_2 forms 1.417 g potassium , a substance used in

Question

The reaction of 0.779 g K with O_2 forms 1.417 g potassium , a substance used in self-contained breathing devices Determine the formula for potassium a.KO_2 b. KO c. K_2 O_2 d. K_2 O e. KO If 4.49 g NaNO_3 is dissolved in enough water make 250.0 mL of solution, what is the molarity of to sodium nitrate solution? a. 1.80 times 10^-2 M b. 5.28 times 10^-2 M c. 2.11 times 10^-1M d. 1.32 times 10^-2 If 25.00 mL of 1.50 M HCI(aq) is diluted with water to a volume of 750.0 mL, what is the molarity of the diluted HCl (aq)? a. 2.22 times 10^-2 M b. 5.00 times 10^-2 c. 2.07 times 10^-3 M d. 4.50 times 10^3 M e. 1.35 times 10^3 M

Explanation / Answer

17) Ans. (a) KO2

18) Ans. (c)

no.of moles - mass in grams / molar mass - 4.49 g / 85 g/ mol

molarity - no.of moles / volume in litre - 4.49 /(85 x 0.250) - 0.211 M

19) Ans (b) 5.00 x10^-2

25 ml to 750 ml means 30 Times dilution.I.e)1.50 M /30 - 0.05 M

20) Ans (d) 0.27

M1 V1 = M2 V2 ,

V1 = 0.20 M x 4.0 L/3.0 M=0.27 L

21) Ans (a) 1.5 x 10^-13

-log H+= 12.83

H+ = 10^(-12.83)= 1.5 x 10^-13  

22) Ans (b) 4.01 L

according to stoichiometry 65.3 g Zn needs 73 g HCl.

so 25 g Zn needs 73 x 25 /65.3 = 27.95 g HCl

no.of moles of HCl = 27.95/36.5 = 0.77 moles of HCl

3.05 M HCl means 3.05 moles in 1 litre.

So 0.77 moles in 3.05/0.77= 4

That is four times dilution I.e) 4.01 L

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