Tag: chemistry

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Multiple choice chemistry the p-block elements - group 13 study of orthoboric acid some important compounds of boron study of boron

Which of the following statements about $H _3BO _3$ is not correct?

  1. It is a strong tribasic acid

  2. It is prepared by acidifying an aqueous solution of borax

  3. It has a layer structure in which planar borate ions are joined by hydrogen bonding

  4. None of these
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Boric acid, also called hydrogen borate is a weak, monobasic Lewis acid of boron. So it is not a strong tribasic acid. Remaning all options are correct

Hence option $A$ is correct.

Multiple choice chemistry the p-block elements - group 13 study of orthoboric acid some important compounds of boron study of boron

Which one of the following statements about $H _3BO _3$ is not correct?

  1. It is a strong tribasic acid

  2. It is a prepared by acidifying an aqueous solution of borax
  3. It has a layer structure in which planar $BO _3$ units are joined by hydrogen bonds

  4. It does not act as proton donor as it acts as a Lewis acid by accepting hydroxyl ions
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

It is weak monoprotic acid and it does not act as proton donor but removes proton from water.

Multiple choice chemistry the p-block elements - group 13 study of orthoboric acid some important compounds of boron study of boron

$B _{2}Ca _{6}O _{11}+ Na _{2}CO _{3}\overset{\Delta }{\rightarrow}\left [ X \right ]+CaCO _{3}+NaBO _{2}$ (unbalanced equation)
Correct choice(s) for [X] is/are:

  1. structure of anion of crystalline [X] has one boron atom sp$^{3}$ hybridised and other three boron atoms sp$^{2}$
    hybridised

  2. X with NaOH (aq.) gives a compound which on reaction with hydrogen peroxide in alkaline medium yields
    a compound used as brightner in soaps
  3. hydrolysis of [X] with HCl or H$ _{2}$SO$ _{4}$ yields a compound which on reaction with HF gives fluoroboric acid

  4. [X] on heating with chromium salts in oxidising flame gives green coloured bead in cold
Reveal answer Fill a bubble to check yourself
B,C,D Correct answer
Explanation

Compound [X] is Na$ _{2}$B$ _{4}$O$ _{7}$
(A) two boron atoms are $sp^{2}$ while other two boron atoms are $sp^{3}$ hybridised.
(B) product is sodium peroxoborate which is used as brightner in soaps.
(C) $H _{3}BO _{3}$ is formed which with HF gives $HBF _{4}$.
(D) Green bead in oxidising as well as in reducing flame in cold.

Multiple choice chemistry measurement and data processing and analysis uncertainties and errors, graphical techniques uncertainty in measurement measurement of properties

Given the numbers $786$, $0.786$ and $0.0786$. The number significant figures for the numbers is :

  1. $3$, $4$ and $5$ respectively
  2. $3$, $3$ and $3$ respectively
  3. $3$, $3$ and $4$ respectively
  4. $3$, $4$ and $4$ respectively
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

For 786, all three digits are significant. For 0.786, leading zeros are not significant, so there are 3. For 0.0786, leading zeros are not significant, so there are 3.

Multiple choice chemistry measurement and data processing and analysis uncertainties and errors, graphical techniques uncertainty in measurement measurement of properties

How many significant digits does the measurement $124.04g$ possess?

  1. $1$
  2. $2$
  3. $3$
  4. $4$
  5. $5$
Reveal answer Fill a bubble to check yourself
E Correct answer
Explanation

The number of single digits that are important in the coefficient of an expression in scientific notation is termed as significant number.

The significant digits in the given number are $1,2,4,0$ and $4$. Therefore, $5$ significant digits are there in the number $124.04g$.

Multiple choice chemistry measurement and data processing and analysis uncertainties and errors, graphical techniques uncertainty in measurement measurement of properties

Which of the following numbers has 1 significant figure?

  1. 0.060

  2. 0.60

  3. 6.0

  4. 60
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

There are three rules on determining how many significant figures are in a number: Non-zero digits are always significant. Any zeros between two significant digits are significant. A final zero or trailing zeros in the decimal portion ONLY are significant.


Hence, only option D has one significant figure and all others have 2 significant figures.

Hence, the correct option is $\text{D}$