What is the molarity of a solution that results when 21.3 g of (NH_4)_3PO_4 is d

Question

What is the molarity of a solution that results when 21.3 g of (NH_4)_3PO_4 is dissolved in H_2O and diluted to exactly 250.0 mL? a. 100 M b. 1.50 times 10^-3 M c. 0.572 M d. 1.61 times 10^-4 M If you have 50.0 mL of 4.0 M NaOH and you want 0.50 M NaOH. How much water in mL do you need to make the 0.50 M NaOH solution? a. 350 mL b. 100 mL c. 150 mL d. 300 mL Zinc reacts with acids to produce H_2 gas. If you have 10.00 g of Zn, what volume of 1.50 M HC1 is required to convert the Zn completely? Zn(s) + 2 HCl(aq) rightarrow ZnCl_2(aq) + H_2(g) a. 0.134 L b. 0.122 L c. 0.342 L d. 0.204 L 76.80 g of malic acid (C_4H_6O_5) requires 34.56 mL of 0.663 M NaOH for titration. Calculate the amount (# of mole) of acid titrated and what is the weight % of malic acid? Balanced Chemical eq. is: C_4H_6O_5(aq) rightarrow Na_2C_4H_4O_5(aq) + 2 H_2O_(liq) a. 0.0230 mol and 2.10% b. 0.0115 mol and 2.01% c. 0.0118 mol and 3.01% d. 0.1151 mol and 2.01% What is the oxidation number of Cr in a compound, Cr_2O_7^-2? a. -3 b. +4 c. -5 d. +6

Explanation / Answer

5. Answer C

Molarity = (Wt/mol.wt)*(1000/V(mL))

M = (21.3g/149g/mol)(1000/250mL) = 0.572M

6. Answer A
M1V1=M2V2

4.0M*50.0mL=0.5M*V2

V2=4.0M*50.0mL/0.5M =400mL

Volume of water to be added = 400-50=350mL

7. Answer D

Zn + 2 HCl ------> ZnCl2 + H2

1mole Zn=2moles HCl

10g Zn = 10g/65.38g/mol = 0.157mole

0.157mole of Zn requires 2*0.157 = 0.31mole HCl

molarity (M) = moles/L, therefore L = moles/molarity = 0.31/1.50 = 0.206L

8. Answer B

Amount of NaOH used = 0.663M*0.03456L = 0.0229 mol NaOH

Amoun tof acid titrated = 0.0229mol*1mol acid/2mol NaOH = 0.0115 mol acid

Mass of acid titrated = M*mol. wt = 0.0115M*134g = 1.54g

weight % of malica acid = 1.54/76.80*100 = 2.01%

9. ANswer D

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