156 gm of cane sugar is strongly heated in a test tube. The number of moles of water lost is
Answers
Explanation:
Materials:
Aluminum foil
Pen
Scissors
Ruler
Sugar
Salt
Measuring spoons
Large candle
Magnifying glass
Matches
Tongs
Metal dish
Notebook
Pencil
Grown-up
Procedure:
Use a ruler and a pen to measure and mark a three inch squre on the aluminum foil.
Cut the square out.
Stick your thumb in the middle of the square and use your other hand to lift the sides of the foil around your thumb, creating a miniature boat shape.
Measure 1/4 teaspoon of sugar.
Put the sugar in the foil boat.
Study the sugar with your magnifying glass. Can you see each individual sugar piece?
What do you think will happen when you heat the sugar? Write your guess, or hypothesis, in your notebook.
Have a grown-up use matches to light the candle.
Put the metal dish next to the candle.
Using the tongs, hold the foil boat just above the flame.
Slowly count to ten as you observe what happens to the sugar. Don't just use your your eyes -- use your nose to note how the sugar smells.
Remove the foil boat and blow out the candle.
Set the heated sugar on the metal dish.
Use your magnifying glass to study the heated sugar.
Did the sugar do what you expected?
Results:
The sugar should have melted down to a liquid form and turned a light brown color. Once the sugar had been heating for awhile, it should have turned black and started producing wisps of smoke. Once you transferred the sugar from the flame to the metal dish, the sugar would be blackish brown, solid and surrounded by black soot.
then answe
=
m
solute
m
solution
⋅
100
In your case, the mass of the solution will be
m
solution
=
m
glucose
+
m
water
m
solution
=
20
+
150
=
170 g
This means that you get
%w/w
=
20
g
170
g
⋅
100
=
11.8%
The density of this solution will thus be
ρ
=
1.045 g/mL
Use glucose's molar mass to determine how many moles you have
20
g
⋅
1 mole glucose
180.16
g
=
0.111 moles glucose
The solution's volume will be
170
g
⋅
1 mL
1.045
g
=
162.7 mL
This means that its molarity is - do not forget to convert the volume to liters!
C
=
n
V
=
0.111 moles
162.7
⋅
10
−
3
L
=
0.68 M
A solution's molality is defined as the number of moles of solute divided by the mass of the solvent - in kilograms! This means that you have
b
=
n
m
water
=
0.111 moles
150
⋅
10
−
3
kg
=
0.74 molal
To get the mole fraction of sucrose, you need to know how many moles of water you have present. Once again, use water's molar mass
150
g
⋅
1 mole water
18.02
g
=
8.24 moles water
The total number of moles the solution contains is
n
total
=
n
glucose
+
n
water
n
total
=
0.111
+
8.24
=
8.351 moles
This means that the mole fraction of sucrose, which is defined as the number of moles of sucrose divided by the total number of moles in the solution, will be
χ
sucrose
=
n
sucrose
n
total
=
0.111
moles
8.351
moles
=
0.013
Given:
The mass of cane sugar = 156 gm
To Find:
The number of moles of water lost upon heating.
Calculation:
- Cane sugar is sucrose (C12H22O11).
- The molar mass of sucrose = 342 gm
- No of moles of sucrose in 156 g sugar = 156/342 = 0.456 moles
- Upon heating, the chemical reaction is given as:
C12H22O11 → 12 C + 11 H2O
⇒ The moles of water given by 1 mole of sucrose = 11
⇒ The moles of water given by 0.456 moles of sucrose = 11 × 0.456 = 5.016