Chemistry Questions

Scarbo

2010-12-25 7:08 am

Q/ Which of the following solutions has the greatest mass of solute? (Relative atomic masses: H=1.0, O=16.0, Na=23.0) ANS: B A. 10.0 cm3 of 3.00 M sodium hydroxide solution B. 20.0 cm3 of 2.00 M sodium hydroxide solutionC. 80.0 cm3 of 6.00 g dm-3 sodium hydroxide solutionD. 1o0.0 cm3 of 8.00 g dm-3 sodium hydroxide solutionQ/ Which of the following solutions contains the greatest number of ions? ANS: A A. 60 cm3 of 0.1 M Na3PO4 (aq) B. 60 cm3 of 0.1 M K2SO4 (aq)C. 90 cm3 of 0.05 M KNO3 (aq)D. 120 cm3 of 0.05 M AgNO3 (aq)Q/ Which of the following solutions contains the smallest number of ions? ANS: A A. 30 cm3 of 2 M HCl(aq) B. 40 cm3 of 3 M NaCl (aq)C. 50 cm3 of 2 M Na2CO3 (aq)D. 60 cm3 of 15 M H2SO4 (aq)Q/ Which of the following procedures will not give a solution of sodium carbonate with a molarity of exactly 1.00 M? (Relative atomic masses: C=12.0, O=16.0, Na=23.0) ANS: AA. Dissolve 10.6 g of sodium carbonate in 10.0 cm3 of water.B. Dissolve 10.6 g of sodium carbonate in 50.0 cm3 of water and more water up to 100.0 cm3.C. Dissolve 106 g of sodium carbonate in 1000.0 cm3 of water.D. Dissolve 106 g of sodium carbonate in 500.0 cm3 of water and then add another 500.0 cm3 water.

回答 (1)

己式庚辛

2010-12-25 8:49 am

✔ 最佳答案

1.
A: no. of mole = volume x molarity = (10/1000) x 3 = 0.03 mole
mass = molar mass x no. of mole = (23+16+1) x 0.03 = 1.2 g
B: no. of mole = 0.04 mole
mass = 1.6 g
C: mass = volume x concentration = (80/1000) x 6 = 0.48 g
D: mass = (100/1000) x 8 = 0.8 g

2.
first write the dissociation equations:
Na3PO4 ------> 3Na(+) + PO4(3-) one mole of salt gives 4 mole of ions
K2SO4 ------> 2K(+) + SO4(2-) one mole of salt gives 3 moles of ions
KNO3 ------> K(+) + NO3(-) one mole of salt gives 2 moles of ions
AgNO3 ------> Ag(+) + NO3(-) one mole of salt gives 2 moles of ions

A: conc. of salt = molarity x volume = 0.1 x (60/1000) = 0.006 mole
no of mole of ions = 0.006 x 4 = 0.024 mole
B: conc. = 0.006 mole
ion = 0.018 mole
C: conc. = 0.05 x (90/1000) = 0.0045 mole
ion = 0.0090 mole
D: conc. = 0.006 mole
ion = 0.0120 mole

3.
similar to question 2.
first write down the acid ionization / salt dissociation equations;
then calculate no. of mole of ions given per mole of acid;
finally calculate the concentration of salt and ions.

4.
B, C and D are in fact talking about same thing. so neither one could be the answer ----
D: same mass (106g) of sodium carbonate is added into total volume of 1000cm3 of water, so it's same as C.
B: both mass and total volume of water (106g --> 10.6g, 1000cm3 --> 100cm3) are reduced to one-tenth, so concentration remains the same.

nonetheless, i'll include the method of calculation of concentration.
A: mass = 10.6 g
no. of mole = 10.6 / (23x2 + 12 + 16x3) = 0.1 mole
volume of water = 10cm3 = 0.001dm3
thus molarity = n. of mole / volume = 0.1 / 0.001 = 10 M

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