Tag: chemistry

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Multiple choice hydrogen ion scale or the ph scale inorganic analysis chemical analysis and investigation practical work chemistry

pH can be detected by :

  1. litmus paper

  2. pH meter

  3. phenolphthalein

  4. all of the above
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

Indicators may be used to measure pH, by making use of the fact that their color changes with pH. Visual comparison of the color of a test solution with a standard color chart provides a means to measure pH accurate to the nearest whole number. Litmus paper is most widely used to check the pH of a solution. pH meter gives the strength of acidity or basicity of a solution. Phenolphthalein can be used to distinguish between acids and bases.

Multiple choice hydrogen ion scale or the ph scale inorganic analysis chemical analysis and investigation practical work chemistry
Unknown metal Appearance Reactions with dilute HCl Reaction with dilute HNO$ _3$
 (1) Dull gray solid with white oxide coating  Dissolved with bubbles of clear gas  Dissolved with bubbles of clear gas
 (2) Solid; lustrous smooth silver-gray surface No reaction  Dissolved with bubbles of orange gas

The addition of dilute HNO$ _3$ to unknown metal (2) produced an orange gas. Which of the following is the orange gas?

  1. Cl$ _2$
  2. H$ _2$
  3. O$ _2$
  4. CO$ _2$
  5. NO$ _2$
Reveal answer Fill a bubble to check yourself
E Correct answer
Explanation

The addition of dilute $HNO _3$ to unknown metal (2) (silver metal) produced an orange gas nitrogen dioxide $\displaystyle (NO _2)$.
Note: Various gases have following colours.
$Cl _2-$ green
$H _2-$ colorless
$O _2-$ colorless
$CO _2-$ colorless
$NO _2-$ orange/brown

Multiple choice hydrogen ion scale or the ph scale inorganic analysis chemical analysis and investigation practical work chemistry

Which of the following would seperate $\displaystyle { H } _{ 2 }{ S }$ at pH < 7 ?

  1. $\displaystyle { Zn }^{ 2+ },{ Co }^{ 2+ }$
  2. $\displaystyle { Cu }^{ 2+ },{ Cd }^{ 2+ }$
  3. $\displaystyle { Cu }^{ 2+ },{ Cr }^{ 3+ }$
  4. $\displaystyle { Cu }^{ 2+ },{ As }^{ 3+ }$
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

$\displaystyle { H } _{ 2 }{ S }$ would separate $\displaystyle { Cu }^{ 2+ },{ Cr }^{ 3+ }$ at pH<7 .
$Cu^{2+} +  H _2S \uparrow \rightarrow  \underset {black  ppt} {CuS} + 2H^+$

Multiple choice hydrogen ion scale or the ph scale inorganic analysis chemical analysis and investigation practical work chemistry

pH stands for :

  1. power of hydrogen

  2. power of hydroxide

  3. purity of hydrogen

  4. purity of hydroxide
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

pH is the negative log of hydrogen ion concentration in a water-based solution. The term 'pH' was first described by Danish biochemist Soren Peter Lauritz Sorensen in 1909. pH is an abbreviation for 'power of hydrogen' where 'p' is short for the German word for power and 'H' is the element symbol for hydrogen.

Multiple choice hydrogen ion scale or the ph scale inorganic analysis chemical analysis and investigation practical work chemistry

Which of the following liquids can be used to check pH?

  1. Phenolphthalein

  2. Bromothymol blue
  3. Both $A$ and $B$

  4. None of the above
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

A pH indicator is a halochromic chemical compound added in small amounts to a solution so the pH (acidity or basicity) of the solution can be determined visually. Hence, a pH indicator is a chemical detector for hydronium ions ($H _3O^+$) or hydrogen ions ($H^+$). Bromophenol blue is used as a pH indicator, a color marker, and a dye. As an acid-base indicator, its useful range lies between pH 3.0 and 4.6. It changes from yellow at pH 3.0 to blue at pH 4.6; this reaction is reversible. Phenolphthalein is often used as an indicator in acid-base titrations. For this application, it turns colorless in acidic solutions and pink in basic solutions.

Multiple choice hydrogen ion scale or the ph scale inorganic analysis chemical analysis and investigation practical work chemistry

State True or False.
The strength of acidity or basicity is not given by $pH$ paper.

  1. True

  2. False
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

$pH$ paper is the litmus paper which helps in identification of whether the solution is acidic or basic in nature. It does not help to determine the strength of acidity or basicity of a solution.

Multiple choice hydrogen ion scale or the ph scale inorganic analysis chemical analysis and investigation practical work chemistry


$\begin{matrix}&pH=X\Cr _2O _7^{2-}&\rightleftharpoons&CrO _4^{2-}\(orange)&pH=Y&(green)\end{matrix}$
This change is based on change in $pH$. Probable values of $X$ and $Y$ cannot be :

  1. 8, 6

  2. 8, 10

  3. 4, 6
  4. change is independent of $pH$
Reveal answer Fill a bubble to check yourself
B,C Correct answer
Explanation

$\begin{matrix}&pH=X= 8  \ or \ 4 \ (less\  than \ Y) \Cr _2O _7^{2-}&\rightleftharpoons&CrO _4^{2-}\orange&pH=Y= 10\  or \ 6  \ (more\  than\  X) &green\end{matrix}$

As dichromate ion changes to chromate in acidic medium( less pH) , whereas chromate changes to dichromate in basic medium ( higher pH)
                             Lower pH (acidic medium) $\rightarrow$
$ Cr _2O _7^{2-}<========================>CrO _4^{2-}$
                            $\leftarrow$ Higher pH ( basic medium)

Multiple choice hydrogen ion scale or the ph scale inorganic analysis chemical analysis and investigation practical work chemistry
Unknown metal Appearance Reactions with dilute HCl Reaction with dilute HNO$ _3$
  (1) Dull gray solid with white oxide coating  Dissolved with bubbles of clear gas  Dissolved with bubbles of clear gas
  (2) Solid, lustrous smooth silver-gray surface No reaction  Dissolved with bubbles of orange gas

Which of the following represents unknown metal (1)  ?

  1. Mercury

  2. Copper

  3. Zinc

  4. Iron

  5. Silver
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

Unknown metal (1) could be zinc as it is dull gray solid with white oxide coating.
Note: Mercury is a liquid, copper is brownish, iron has orange brown coating of oxide (rust) and silver has gray-black colour.

Multiple choice hydrogen ion scale or the ph scale inorganic analysis chemical analysis and investigation practical work chemistry

$\displaystyle \underset {orange}{Cr _2O _7^{2-}}\,\overset {pH=x}{ \underset {pH = y}{\leftrightarrows}}\, \underset {green}{CrO _4^{2-}}$. 


This change is based on change in pH. 

Find values of x and y  :

  1. $8, 6$
  2. $8, 10$
  3. $4, 6$

  4. change is independent of pH
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

The process involves the equilibrium between chromate (VI), dichromate (VI) and hydrogen ions:


$2{ Cr{ O } _{ 4 }^{ 2- } } _{ \left( aq. \right)  \left( yellow \right)  }+2{ { H }^{ + } } _{ \left( aq. \right)  }\rightleftharpoons { { Cr } _{ 2 }{ O } _{ 7 }^{ 2- } } _{ \left( aq. \right)  \left( orange \right)  }+{ { H } _{ 2 }O } _{ \left( l \right)  }$

The addition of acid encourages the equilibrium towards the right (pH=6), producing more orange colored dichromate (VI) ions. The addition of hydroxide ions causes the concentration of hydrogen ions to decrease, and this brings the equilibrium back to the left-hand side, regenerating yellow chromate (VI) ions.