What will be the mass percent of a solution containing 30 grams of common salt into 20g of water?

The molar concentration unit [mol/ L (M)] is a conventionally widely used as concentration method. It is the number of moles of target substance (solute) dissolved in 1 liter of solution. Here is how to calculate the concentration.

(Weight of 1 liter solution) x (purity) ÷ molecular weight
[Specific gravity of solution (g/mL) x 1,000 (mL) x Purity (w/w%) /100 ÷ Molecular weight]

For example, let's calculate the molar concentration of 2-mercaptoethanol (HSCH2CH2OH). The necessary information is as follows.

Specific gravity (or density) = 1.114 g/mL
Purity (or content) = 100 w/w% (assumed)
Molecular weight = 78.13

By calculating this value by applying this value to the above equation, you can know the molar concentration.
1.114 g/mL x 1,000mL x 100w/w%/100 ÷ 78.13 = 14.26mol/L

In order to caluculate the concentration like above, it is necessary to know three points of "specific gravity (or density)", "purity (or content)" and "molecular weight". The table below is a quick reference chart of common acid and base concentrations. In acid and alkali, there is a use for "neutralization titration", "normality (N)" is often used.

【Quick reference chart of common acid and base concentrations】

Compound	Molecular formula	Molecular weight	Purity (w/w％)	Specific gravity (20℃)	Concentration (mol/L)	Equivalent	Normality (N)
Hydrochloric acid	HCl	36.46	20%	1.10	6.0	1	6.0
35%	1.17	11.2	11.2
Nitric acid	HNO3	63.01	60%	1.37	13.0	1	13.0
65%	1.39	14.3	14.3
70%	1.41	15.7	15.7
Sulfate	H2SO4	98.08	100%	1.83	18.7	2	37.3
Phosphoric acid	H3PO4	98.00	85%	1.69	14.7	3	44.0
90%	1.75	16.1	48.2
Acetate	CH3COOH	60.05	100%	1.05	17.5	1	17.5
Perchloric acid	HClO4	100.46	60%	1.54	9.2	1	9.2
70%	1.67	11.6	11.6
Hydrogen peroxide water	H2O2	34.01	30%	1.11	9.8	-
35%	1.13	11.6
Ammonia water	NH3	17.03	25%	0.91	13.4	1	13.4
28%	0.90	14.8	14.8

【Quick reference of concentration and unit】

●How to express concentration of solution

Expression	Commentary
Weight percent concentration	"g number" of solute in 100g solution. Expressed as w/w%, wt%, and % for density in many cases.
Volume percent concentration	"m number" of solute in 100m solution. Expressed as v/v% when mixture or solute is liquid.
Weight versus volume percent concentration	"g number of solute in 100m of solution. Expressed as w/v%.
Normality	Gram equivalent number of solute in 1L solution. Expressed as N for capacity analysis.
Volume specific concentration	Concentration indirectly expressed by the volume ratio of diluting the liquid reagent. It is used in JIS and others. Example: Sulfuric acid (1 + 2) → Sulfuric acid is shown diluted with 2 volumes of water.
Weight ratio concentration	Concentration indirectly expressed by weight ratio at which solid reagent is dissolved. It is used in JIS and others. Example: Sodium chloride (1 + 19) →Dissolved in 19 weight of water with respect to 1 of NaCl.
Molarity	Mol number of target substance (solute) in 1L of solution. Expressed as mol/ or M.

●Prefix representing multiple

Express bigness	Express smallness
100 =102	h（Hecto）	1/100 =10-2	c（Centi）	％（Percent）
1000 =103	k（Kilo）	1/1000 =10-3	m（Milli）	‰（Permili）
100万 =106	M（Mega）	1/100万 =10-6	μ（Micro）	ppm
1 Billion =109	G（Giga）	1/10Billion =10-9	n（Nano）	ppb
1 Trillion =1012	T（Tera）	1/1 Trillion =10-12	p（Pico）	ppt
1000 Trillion =1015	p（Peta）	1/1000 Trillion =10-15	f（Femto）	ppq

●ppmConversion table

ppb	ppm	%	mg/g	mg/L
1,000	1	0.0001	0.001	1
10,000	10	0.001	0.01	10
100,000	100	0.01	0.1	100
1,000,000	1,000	0.1	1	1,000
10,000,000	10,000	1	10	10,000

Chemistry Solutions Percent Concentration

The percentage concentration of any solution is most commonly expressed as mass percent:

Mass % of any component of the solution =
(Mass of the component in the solution / Total mass of the solution) x 100

Other methods are:

Volume % of a component =
(Volume of the component/Total volume of the solution) x 100
1. Mass by volume percentage:
  It is the mass of solute dissolved in 100 mL of the solution.
i.e. Mass by Volume percentage =
(Mass of solute in grams/Volume of solution in mL) x 100

Here's a point to be kept in mind :
Whenever we say mass or volume of the solution, you need to add the respective masses and volumes of ALL the components of the solution. Do NOT commit the error of taking the mass or volume of only the solute or solvent in the denominators of the above expressions.

The concentration of a solution is most of the time expressed as the number of moles of solute present in 1 Liter of the solution (also called molarity )

(There are also other ways to express concentration. Please follow this link. )

EXAMPLE:
(a) If 25 moles of NaCl are present in 100 L of a solution wherein H2O is the solvent, then the concentration of the solution is #25/100=0.25 "mol·L"^-1#.

(b) What is the molarity of a solution prepared by dissolving 15.0 g of sodium hydroxide in enough water to make a total of 225 mL of solution?

Solution
- Calculate the number of moles of solute present.
Moles of NaOH = 15.0 g NaOH × #(1"mol NaOH")/(40.00"g NaOH")# = 0.375 mol NaOH
- Calculate the number of litres of solution present.
Volume = 225 mL × #(1"L")/(1000"mL")# = 0.225 L soln
- Divide the number of moles of solute by the number of litres of solution.
Molarity = #(0.375"mol")/(0.225"L")# = 1.67 mol/L
Let's address the question for both percent concentration by mass and for percent concentration by volume.

Percent concentration by mass is defined as the mass of solute divided by the total mass of the solution and multiplied by 100%. So,

#c% = m_(solute)/(m_(solution)) * 100%#, where

#m_(solution) = m_(solvent) + m_(solute)#

There are two ways to change a solution's concentration by mass
- Adding more solute - making the solution more concentrated;
- Adding more solvent - making the solution more dilute;
Let's take an example to better illustrate this concept. Say we dissolve 10.0g of a substance in 100.0g of water. Our concentration by mass will be

#c% = (10.0g)/(10.0g + 100.0g) * 100% = 9.09%#

Now let's try doubling the mass of the solute; the new concentration will be

#c% = (2 * 10.0g)/(2*10.0g + 100.0g) * 100% = 16.7%#

However, if we keep the mass of the solute at 10.0g and doubled the mass of the solvent (in this case, water), the concentration will be

#c% = (10.0g)/(10.0g + 2*100.0g) * 100% = 4.76%#

The same is true for percent concentration by volume, which is defined as the volume of the solute divided by the total volume of the solution and multiplied by 100%.

#c_(volume)% = V_(solute)/(V_(solute) + V_(solvent)) * 100%#

It's easy to see that manipulating either the volume of the solute or the volume of the solvent (or both) would change the solution's percent concentration by volume.
There are two types of percent concentration: percent by mass and percent by volume.

PERCENT BY MASS

Percent by mass (m/m) is the mass of solute divided by the total mass of the solution, multiplied by 100 %.

Percent by mass = #"mass of solute"/"total mass of solution"# × 100 %

Example

What is the percent by mass of a solution that contains 26.5 g of glucose in 500 g of solution?

Solution

Percent by mass =

#"mass of glucose"/"total mass of solution" × 100 % = (26.5"g")/(500"g")# × 100 % = 5.30 %

PERCENT BY VOLUME

Percent by volume (v/v) is the volume of solute divided by the total volume of the solution, multiplied by 100 %.

Percent by volume = #"volume of solute"/"total volume of solution"# × 100 %

Example

How would you prepare 250 mL of 70 % (v/v) of rubbing alcohol

Solution

70 % = #"volume of rubbing alcohol"/"total volume of solution" × 100 %# × 100 %

So

Volume of rubbing alcohol = volume of solution × #"70 %"/"100 %"# = 250 mL × #70/100#

= 175 mL

You would add enough water to 175 mL of rubbing alcohol to make a total of 250 mL of solution.