the same with all the above dilute solutions,
Table-1
bage,
Reddimus
ntain
Sample
solution
Red im
paper
Blue
paper
Phenolphthalein
solution
Methy
orange
Solution
acid-
city.
etic
HCI
Ito
H.SO.
ΗΝΟ,
CHCOOH
do
NaOH
KOH
Mg(OH)2
NH, OH
Са(ОН),
divis
pur
• What do you conclude from the observations noted in table-1?
Identify the sample as acidic or basic solution.
There are some substances whose odour changes in acidic or basic
media. These are called olfactory indicators.
Let us work with some of such indicators.
area
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Answer:
Explanation:
Molarity
The most common unit of solution concentration is molarity (M).
The molarity of a solution is defined as the number of moles of
solute per one liter of solution. Note that the unit of volume for
molarity is liters, not milliliters or some other unit. Also note
that one liter of solution contains both the solute and the solvent.
Molarity, therefore, is a ratio between moles of solute and liters of
solution. To prepare laboratory solutions, usually a given volume
and molarity are required. To determine molarity, the formula
weight or molar mass of the solute is needed. The following examples illustrate the calculations for preparing solutions.
If starting with a solid, use the following procedure:
• Determine the mass in grams of one mole of solute, the molar
mass, MMs.
• Decide volume of solution required, in liters, V.
• Decide molarity of solution required, M.
• Calculate grams of solute (gs) required using equation 1.
eq. 1. gs = MMs x M x V
• Example: Prepare 800 mL of 2 M sodium chloride.
(MMNaCl = 58.45 g/mol)
gNaCl = 58.45 g/mol x 2 mol/L x 0.8 L
gNaCl = 93.52 g NaCl
Dissolve 93.52 g of NaCl in about 400 mL of distilled water,
then add more water until final volume is 800 mL.
If starting with a solution or liquid reagent:
• When diluting more concentrated solutions, decide what
volume (V2) and molarity (M2) the final solution should be.
Volume can be expressed in liters or milliliters.
Basic Concepts of Preparing Solutions
M• Determine molarity (M1) of starting, more concentrated solution.
• Calculate volume of starting solution (V1) required using equation 2. Note: V1 must be in the same units as V2.
eq. 2. M1V1 = M2V2
• Example: Prepare 100 mL of 1.0 M hydrochloric acid from
concentrated (12.1 M) hydrochloric acid.
M1V1 = M2V2
(12.1 M)(V1) = (1.0 M)(100 mL)
V1 = 8.26 mL conc. HCl
Add 8.26 mL of concentrated HCl to about 50 mL of distilled
water, stir, then add water up to 100 mL.
Percent Solutions
Mass percent solutions are defined based on the grams of solute
per 100 grams of solution.
Example: 20 g of sodium chloride in 100 g of solution is a 20%
by mass solution.
Volume percent solutions are defined as milliliters of solute per
100 mL of solution.
Example: 10 mL of ethyl alcohol plus 90 mL of H2O (making
approx. 100 mL of solution) is a 10% by volume
solution.
Mass-volume percent solutions are also very common. These
solutions are indicated by w/v% and are defined as the grams of
solute per 100 milliliters of solution.
Example: 1 g of phenolphthalein in 100 mL of 95% ethyl
alcohol is a 1 w/v% solution.