2nd exam of the 1st term for 2nd ESO G
Name:
1. Look at the following picture:
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


Date:
What is the name of the separation technique that you see?
What type of substances you separate with this technique?
Write an example of a mixture you would separate with this technique.
Explain how you use this technique to separate the components of a mixture.
(1 point)
2. Centrifugation is used, among other things, to separate the components of blood. Explain this
separation technique.
(0.5 points)
3. You have two liquids, A and B, that can mix. The boiling point of A is 60 ºC and the boiling point of B
is 120 ºC.
 How do you call two liquids that can mix?
 What is the name of the separation technique that you use to separate these two liquids? Explain
it using a picture.
(2 points)
4. a) What is the difference between a pure substance and a mixture?
b) What are the two types of pure substances that exist? What is the difference between them?
c) What are the two types of mixtures that we have studied? What is the difference between them?
d) For exercises 1, 2, 3, 5 and 6 write what type of mixture we are dealing with.
(2 points)
5. Explain crystallization: explain what type of substances you separate with this technique and how.
Write the name of any important lab material that you use.
(0.5 points)
6. You have two liquids that can´t mix.
 How are these kind of liquids called?
 How would you separate them? Write the name of the separation technique you should use and
use a picture to explain it. Write the name of the lab material that you use.
(1 point)
7. You want to prepare 400 cm3 of an aqueous solution of sodium fluoride (a solid that can dissolve in
water). The concentration of the solution that you want to prepare is 24 g/L. What is the mass of sodium
fluoride that you need?
Explain how you would prepare this solution. Write the name of any important lab material that you use.
(1 point)
8. You add water to 4 Hg of sugar until the final volume of the solution is 300 dL. Calculate the
concentration of this solution in g/L. Which is the solute and which is the solvent?
(1 point)
9. Calculate the mass of sodium hydroxide (a solid that can dissolve in water) that is dissolved in 550 mL
of a solution whose concentration is 8 g/L.
(1 point)
2nd exam of the 1st term for 2nd ESO G (answers)
Name:
1. Look at the following picture:




Date:
What is the name of the separation technique that you see?
What type of substances you separate with this technique?
Write an example of a mixture you would separate with this technique.
Explain how you use this technique to separate the components of a mixture.
(1 point)
The separation technique is filtration.
You separate a solid from a liquid when the solid doesn´t dissolve in the liquid.
An example of a mixture you would separate with this technique is sand and water.
You pour the mixture on the funnel, which has a filter paper. The insoluble solid will remain on the filter
paper while the liquid will fall to the beaker below.
2. Centrifugation is used, among other things, to separate the components of blood. Explain this
separation technique.
(0.5 points)
You make the mixture spin very fast in a centrifuge. The centripetal force makes the components of the
mixture separate.
3. You have two liquids, A and B, that can mix. The boiling point of A is 60 ºC and the boiling point of B
is 120 ºC.
 How do you call two liquids that can mix?
 What is the name of the separation technique that you use to separate these two liquids? Explain
it using a picture.
(2 points)
Two liquids that can mix are called miscible.
The separation technique that you use to separate this mixture is called distillation.
You heat the mixture. When it reaches 60 ºC, A boils but B remains on the flask. A (in gas state) goes up.
When A reaches the refrigerant (cold area) it condenses (transforms into liquid) so it is collected in liquid
state on a different flask.
4. a) What is the difference between a pure substance and a mixture?
b) What are the two types of pure substances that exist? What is the difference between them?
c) What are the two types of mixtures that we have studied? What is the difference between them?
d) For exercises 1, 2, 3, 5 and 6, write what type of mixture we are dealing with.
(2 points)
a) A pure substance is a type of matter that can´t be separated into simpler ones using physical methods.
A mixture is formed by two or more pure substances and we can separate the components of a mixture
using physical methods.
b) We have simple substances and compounds. Simple substances can´t be decomposed into simpler ones
using chemical methods. But compounds are formed by simpler pure substances. We can separate a
compound into its simpler substances using chemical methods.
c) Heterogeneous mixtures: the physical properties of a heterogeneous mixture vary from one part of the
mixture to another. In most cases, you can see the components of the mixture.
Homogeneous mixtures: the physical properties of a homogeneous mixture are the same in all parts of the
mixture. You can´t see the components of the mixture.
d) 1: Heterogeneous
2: Heterogeneous
3: Homogeneous
5: Homogeneous
6: Heterogeneous
5. Explain crystallization: explain what type of substances you separate with this technique and how.
Write the name of any important lab material that you use.
(0.5 points)
You separate a solid from a liquid when the solid dissolves in the liquid. You pour the solution on a
crystallising dish and after a few days the water will have evaporated. On the crystallising dish you will
find crystals of the solid.
6. You have two liquids that can´t mix.
 How are these kind of liquids called?
 How would you separate them? Write the name of the separation technique you should use and
use a picture to explain it. Write the name of the lab material that you use.
(1 point)
These liquids are called immiscible.
I would use a technique called “decantation” to separate them. I use a separating funnel for that. In the
separating funnel, the denser liquid remains below and the less dense liquid remains on top of the other
liquid. You open the separating funnel and the denser liquid will fall to a beaker below. When you are
about to reach the level of the other liquid, you close the separating funnel so the less dense liquid doesn´t
fall on the beaker below.
One example of immiscible liquids are oil and water. The density of water is bigger than the density of
oil.
7. You want to prepare 400 cm3 of an aqueous solution of sodium fluoride (a solid that can dissolve in
water). The concentration of the solution that you want to prepare is 24 g/L. What is the mass of sodium
fluoride that you need?
Explain how you would prepare this solution. Write the name of any important lab material that you use.
(1 point)
You weigh 9.6 g of sodium fluoride using a scale. Then, you transfer this mass to a beaker, where you
add water (less than 400 mL) and stir until it is dissolved. Then, you transfer the solution to a 400 mL
volumetric flask, where, using a dropper, you add water until you have 400 mL.
8. You add water to 4 Hg of sugar until the final volume of the solution is 300 dL. Calculate the
concentration of this solution in g/L. Which is the solute and which is the solvent?
(1 point)
Water is the solvent. Sugar is the solute.
9. Calculate the mass of sodium hydroxide (a solid that can dissolve in water) that is dissolved in 550 mL
of a solution whose concentration is 8 g/L.
(1 point)