Question

Read the information given in the table and answer the following question.

Solution	pH Value	Reaction with Phenolphthalein solution	Reaction with Methyl orange solution
$HCl$	$1$	No color change.	Turns into red
Distilled water	$7$	No color change.	No color change.
$NaOH$	$13$	Turns into pink color.	Turns into yellow color.
Lemon juice	$2.5$	No color change.	Turns into red color.
$NaCl$	$7$	No color change.	No color change.
Baking Soda	$8$	Turns into pink color.	Turns into yellow color.

a) List out the acids in the above table.
b) What is the nature of the solution which gives pink color with the Phenolphthalein solution?
c) List out the neutral solutions in the above table.
d) Name the strongest acid and the strongest base among the given solutions.

Answer 1

Hint: To solve this problem firstly we should learn about Acid, base, neutral substances etc. also about phenolphthalein and the concept behind them. Then, by using this information, we can easily solve the questions (sub-questions asked in our question) and hence, approach our answer. So, lets know them briefly.

Complete step by step answer:
> Acids: Acids are the substance which are sour in taste which is capable of releasing ${H^ + }$ ion also it turns blue litmus paper to red , the common examples of acid are curd which contain lactic acid, vinegar consist of acetic acid, citrus fruits having citric acid. In pH scale the value of acids are below $7$ as the value decreases the concentration of ${H^ + }$ ions increases hence the acidity increases.
> Bases: Bases are the substances which are bitter in taste , soapy in nature which is capable of releasing $O{H^ - }$ hydroxyl ions also it turns red litmus blue, the common examples of bases are lime water consisting of calcium hydroxide, soaps containing sodium and potassium hydroxide. In pH scale the value of base is above $7$ as the value increases the concentration of hydroxyl ion increases.
> Neutral: These are substances which are neither acid nor basic in nature, there is no color change observed when react with litmus paper also when acid and base react it is capable of forming salt and water also known as neutralization reaction. In pH scale the value of these solutions is $7$ .
> Phenolphthalein: It is a chemical compound which is commonly used as an indicator in acid- base titrations. In acidic solution it is colorless but it shows pink color in basic solution.
a) Acids are: $HCl$ and lemon juice because the pH is less than $7$ .
b) Alkaline or basic solution turns phenolphthalein pink.
c) Neutral solutions: Distilled water and $NaCl$.
d) $HCl$ is the strongest acid and $NaOH$ is the strongest base.

Note:
1- pH scale is a scale which is used to measure how acidic or basic is the solution. It ranges from $0 - 14$ , $7$ denotes the neutral solution. Values which lie in between $1$ to $7$are acidic in nature.
2- In pH scale the value of acids are below $7$ as the value decreases the concentration of ${H^ + }$ ions increases hence the acidity increases .
3- In pH scale the value of base is above $7$ as the value increases the concentration of hydroxyl ion increases.