Some More Gen. Chem Q's

[gwest]

Any would be greatly appreciated!! Thanks

In an experiment 25 g of HCL (g) is dissolved in H2O to make 100mL of an acidic solution. Assuming that the acid completely ionized, what is the pH of the solution?..........................-log[25/(0.1*36)]

What mass of styrene (mm= 104.1) will contain 4.5E20 molecules of styrene?........................7.78E-2g

A liter of solution contains 0.00001 mole of HCL. What is the pH of this solution?.........................5.0

A compund consisting of C, H, & O is known by quanitative analysis to have 38.71% C & 9.68% H. What is the empirical formula of this compound?.........................CH3O

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[vize]

These questions are like basic G Chem!

1. -log [H+] = pH. [H+] = molarity, so 25g/.1L * 1mol/36g = (25/(.1*36))... -log (25/(.1*36))

2. 4.5E20 molecules * (104.1 molar mass/6.022E23 molecules)

3. .00001 = 1 * 10^-5... -log [H+] = 5, which equals 10^-5

4. I don't really feel like doing this one, look up how to find empirical formulas from percent composition

 

[Dr. Konfetka]

A compund consisting of C, H, & O is known by quanitative analysis to have 38.71% C & 9.68% H. What is the empirical formula of this compound?.........................CH3O[/QUOTE]


First find out how much O there is...with rounding I got about 51%

So you have about 39% C, 10% H, and 51% O.

Turn the percents into whole number eg. 39 for 39% and then divide each number by the molar mass of the element. Round again...

C: 39/12= 3
H: 10/1=10
O: 51/16=3

Lastly divide all these numbers by the smallest number, 3 in this case. So you get C-1, H-3, and O-1.

Hope this helps.

 

[Chga]

4. 38.71/12 = 3C 9.68/1 = 9H 52/16 = 3O
so C3H9O3 empirical formula is CH3O
(everything is rounded )