please answer me this chemistry question?

M

Mona

New member
1.What is the concentration of sugar (C12h22o11)in mol/ltr if its 20 g are dissolved in enough water to make a final volume up to 2L?

2.if the density of methanol is 0.793 kg/ltr.what is its volume neeted for making 2.5 L of its 0.25 M solution?

3.What do you mean by significant figures?

4.A sample of drinking water was found to be severely contaminated with chloroform CHCL3,supposed to becarcinogenic in nature. The level of contamination was 15 ppm(by mass)
(i)Express this in % by mass
(ii)Determine the molality of chloroform in water sample

please please answer these ques...thnx..
 
part A,
calculate the molecular weight (MW) of the sugar,then calculate the number of moles for the sugar, n= mass/MW.

for concentration C=n/V, therefore number of moles of sugar/ vol of water = mol/L.

Part B
hope you are familiar with formula , C1 V1 = C2 V2
V1 = C2 *V2/ C1

C1 is ,
( 0.793 * 1000)/39 = Concentraion given in mol/L (or M).

now you have C1 from above, C2 =0.25 M, V2= 2.5L and find V1 from the formula above.

PART C
the minimum number of digits needed to write a given value in scientific notation without loss of accuracy.

PART D
note that
1ppm = 1microgram/1mL, therefore 15 ppm is 15microgram/1 liter of water.
a) ppm=mass of substance/mass of sample * 10^6 = 15 microgram/ 1L *10^6 = X %.

b) convert 15 micrograms into grams, then use the MW to calculate the number of moles, then C=n/V (volume is 1L) therfore n/V =M.

good LUCK
 
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