Mass of solute is 5 g per 100 grams of water what does this mean
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It means that the given solution, for any volume of the water, contains 5% of the solute in it.
For example, 1000grams contains 5% of 1000 grams water or 50grams water.
For example, 1000grams contains 5% of 1000 grams water or 50grams water.
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You've done this kind of calculation earlier - last term in the lesson on composition. You may already be prepared to answer the questions in exercise 2 in your workbook. If so, do that and check your answers at the bottom of the page. If not, read on.
As an example, let's consider a 12% by weight sodium chloride solution. Such a solution would have 12 grams of sodium chloride for every 100 grams of solution. To make such a solution, you could weigh out 12 grams of sodium chloride, and then add 88 grams of water, so that the total mass for the solution is 100 grams. Since mass (unlike volume) is conserved, the masses of the components of the solution, the solute and the solvent, will add up to the total mass of the solution. 12 % NaCl solution = 12 g NaCl
100 g solution
12 g NaCl
(12 g NaCl + 88 g water) = 12% NaCl solution
To calculate the mass percent or weight percent of a solution, you must divide the mass of the solute by the mass of the solution (both the solute and the solvent together) and then multiply by 100 to change it into percent.
Examples (Ex. 1)
Your workbook has some examples of calculations involving weight percent in example 1. An explanation of those examples is given here.
Example 1-a asks, "What is the weight percent of glucose in a solution made by dissolving 4.6 g of glucose in 145.2 g of water?" The way that I recommend you go about doing this is to look at what you need to find, look at what you are given, and determine what the relationship is. Let's start with what you are trying to find, the weight percent of glucose in the solution. What do we need in order to calculate that? We need to divide the weight of glucose by the weight of the solution. We have the weight of glucose, that is 4.6 g. What about the weight of the solution? That is not given, but we can figure it out by adding together the weight of glucose and water to get 149.8 g. Now we can calculate the weight percent of glucose as shown to get 3.1%.
Question:
What is the weight percent of glucose in a solution made by dissolving 4.6 g of glucose in 145.2 g of water?
Analysis:
To get weight percent we need the weight of the solute and the total weight of the solution.
Determine total weight of solution:
4.6 g
+ 145.2 g
149.8 g
glucose
water
solution
Calculate percent:
Weight % glucose =
4.6 g glucose x 100 = 3.1% glucose
149.8 g solution
The next question is a little bit different. You are asked how you would prepare 400 g of a 2.50% solution of salt. You are given 400. g of solution (that is total) and you know that 2.50% of that is going to be salt. You need to find out how much salt you need and how much water you need. You can simply multiply 400. g by 2.50% to find out how much salt there is (shown in the top line), or you can set up the calculation shown on the next line. Either way, you find that you need 10.0 g of salt. Since you need a total mass of 400. g and 10. g of that is salt, the remaining 390. g would have to be water. So, to prepare this solution you would have to mix 10.0 g of salt with 390. g of water.
Question:
How would you prepare 400. g of a 2.50% solution of sodium chloride?
Analysis:
We need to find out how much salt is needed and how much water is needed.
Determine weight of salt:
400. g x 2.50% salt = 10.0 g salt
400. g solution x
2.50 g salt
100 g solution
= 10.0 g salt
Determine weight of water:
400. g
- 10. g
390. g
total
salt
water
Answer:
Dissolve 10.0 g salt in 390. g water.
If you have any questions about these calculations be sure to stop and go over them again or work with the instructor if you need to, so that you can get squared away on how to work these kinds of problems.
Practice (Ex. 2)
Take time now to answer the following questions (also given in exercise 2 in your workbook). The third question, you will note, has an extra twist to it. Take some time to do these now, get some help if you need it and then check your answers below.
practice this same type of question
As an example, let's consider a 12% by weight sodium chloride solution. Such a solution would have 12 grams of sodium chloride for every 100 grams of solution. To make such a solution, you could weigh out 12 grams of sodium chloride, and then add 88 grams of water, so that the total mass for the solution is 100 grams. Since mass (unlike volume) is conserved, the masses of the components of the solution, the solute and the solvent, will add up to the total mass of the solution. 12 % NaCl solution = 12 g NaCl
100 g solution
12 g NaCl
(12 g NaCl + 88 g water) = 12% NaCl solution
To calculate the mass percent or weight percent of a solution, you must divide the mass of the solute by the mass of the solution (both the solute and the solvent together) and then multiply by 100 to change it into percent.
Examples (Ex. 1)
Your workbook has some examples of calculations involving weight percent in example 1. An explanation of those examples is given here.
Example 1-a asks, "What is the weight percent of glucose in a solution made by dissolving 4.6 g of glucose in 145.2 g of water?" The way that I recommend you go about doing this is to look at what you need to find, look at what you are given, and determine what the relationship is. Let's start with what you are trying to find, the weight percent of glucose in the solution. What do we need in order to calculate that? We need to divide the weight of glucose by the weight of the solution. We have the weight of glucose, that is 4.6 g. What about the weight of the solution? That is not given, but we can figure it out by adding together the weight of glucose and water to get 149.8 g. Now we can calculate the weight percent of glucose as shown to get 3.1%.
Question:
What is the weight percent of glucose in a solution made by dissolving 4.6 g of glucose in 145.2 g of water?
Analysis:
To get weight percent we need the weight of the solute and the total weight of the solution.
Determine total weight of solution:
4.6 g
+ 145.2 g
149.8 g
glucose
water
solution
Calculate percent:
Weight % glucose =
4.6 g glucose x 100 = 3.1% glucose
149.8 g solution
The next question is a little bit different. You are asked how you would prepare 400 g of a 2.50% solution of salt. You are given 400. g of solution (that is total) and you know that 2.50% of that is going to be salt. You need to find out how much salt you need and how much water you need. You can simply multiply 400. g by 2.50% to find out how much salt there is (shown in the top line), or you can set up the calculation shown on the next line. Either way, you find that you need 10.0 g of salt. Since you need a total mass of 400. g and 10. g of that is salt, the remaining 390. g would have to be water. So, to prepare this solution you would have to mix 10.0 g of salt with 390. g of water.
Question:
How would you prepare 400. g of a 2.50% solution of sodium chloride?
Analysis:
We need to find out how much salt is needed and how much water is needed.
Determine weight of salt:
400. g x 2.50% salt = 10.0 g salt
400. g solution x
2.50 g salt
100 g solution
= 10.0 g salt
Determine weight of water:
400. g
- 10. g
390. g
total
salt
water
Answer:
Dissolve 10.0 g salt in 390. g water.
If you have any questions about these calculations be sure to stop and go over them again or work with the instructor if you need to, so that you can get squared away on how to work these kinds of problems.
Practice (Ex. 2)
Take time now to answer the following questions (also given in exercise 2 in your workbook). The third question, you will note, has an extra twist to it. Take some time to do these now, get some help if you need it and then check your answers below.
practice this same type of question
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