Chemistry Questions

Scarbo

2010-12-25 7:07 am

Q /1.0 mole of magnesium chloride and 1.5 moles of sodium chloride are dissolved in water and the solution is made up to 700.0 cm3. What is the concentration of the chloride ion in the solution? ANS: 5.00M Q/ 42.0 cm3 of water are added to 35.0 cm3 of sodium hydroxide solution so that the new molarity of the solution is 2.10 M. What is the molarity of the original solution? ANS: 4.62 MQ/ When 50.0 cm3 of 0.0100 M sodium hydroxide solution is mixed with 10.0 cm3of 0.100 M sodium hydroxide solution, what is the concentration of sodium hydroxide solution? ANS: 0.0250 MQ/ Solution X is prepared by mixing 100.0 cm3 of 2.50 M Na2 Co3 (aq) with 150.0 cm3 of 1.00 M NaCl (aq). What is the concentration of Na+ (aq) ion in X? ANS: 2.60 MQ/ A solution is prepared by mixing 100.0 cm of 2.00 M Na2NO3 (aq) with 50.0 cm of 0.250 M Zn(NO3) (aq) . What is the concentration of NO3 (aq) ion in the solution? ANS: 1.50 M

How can I get the answer?

回答 (1)

己式庚辛

2010-12-25 9:01 am

✔ 最佳答案

1.
first write the dissociation equations:
MgCl2 ------> Mg(2+) + 2Cl(-)
NaCl ------> Na(+) + Cl(-)

no. of mole of chloride ions given by MgCl2 = 1 mole x 2 = 2 mole
no. of mole of chloride ions given by NaCl = 1.5 mole x 1 = 1.5 mole
total no. of mole of chloride = 3.5 mole
molarity = no. of mole / volume = 3.5 / (700/1000) = 5 M

2.
new volume = 42+35 = 77 cm3
molarity = 2.1M
thus no. of mole of ions = 2.1 x (77/1000) = 0.1617 mole

original volume = 35 cm3
molarity = no. of mole / volume = 0.1617 / (35/1000) = 4.62 M

3.
again, first calculate no. of mole of NaOH in EACH solution;
calculate the final volume of mixture;
calculate molarity using total n. of mole and total volume.

4.
same. write down equations, calculate no. of mole of sodium ions in each solution;
calculate total volume and total no. of mole of sodium ions;
calculate new molarity using volume and no. of mole ----
molarity = no. of mole / volume

5.
same as 4. first two examples should have given you enough guidelines on how to tackle with this kind of problems. it should not be difficult as long as you understand the examples above.
ask again if you really have some more difficulties in following the steps.

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