1
GATE CE 2025 Set 2
Numerical
+2
-0

The analyses results of a water sample are given below. The non-carbonate hardness of the water (in $\mathrm{mg} / \mathrm{L}$ ) as $\mathrm{CaCO}_3$ is __________ (in integer).

$$ \begin{aligned} & \mathrm{Ca}^{2+}=150 \mathrm{mg} / \mathrm{L} \text { as } \mathrm{CaCO}_3 \\ & \mathrm{Mg}^{2+}=40 \mathrm{mg} / \mathrm{L} \text { as } \mathrm{CaCO}_3 \\ & \mathrm{Fe}^{2+}=10 \mathrm{mg} / \mathrm{L} \text { as } \mathrm{CaCO}_3 \\ & \mathrm{Na}^{+}=50 \mathrm{mg} / \mathrm{L} \text { as } \mathrm{CaCO}_3 \\ & \mathrm{~K}^{+}=10 \mathrm{mg} / \mathrm{L} \text { as } \mathrm{CaCO}_3 \\ & \mathrm{CO}_3{ }^{2-}=120 \mathrm{mg} / \mathrm{L} \text { as } \mathrm{CaCO}_3 \\ & \mathrm{HCO}_3{ }^{-}=30 \mathrm{mg} / \mathrm{L} \text { as } \mathrm{CaCO}_3 \end{aligned} $$

$\mathrm{Cl}^{-}=50 \mathrm{mg} / \mathrm{L}$ as $\mathrm{CaCO}_3$; Other anions were not analysed.

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2
GATE CE 2025 Set 1
MCQ (More than One Correct Answer)
+2
-0

$\mathrm{MgCl}_2$ and $\mathrm{CaSO}_4$ salts are added to 1 litre of distilled deionized water and mixed until completely dissolved. Total Dissolved Solids (TDS) concentration is $500 \mathrm{mg} / \mathrm{l}$, and Total Hardness (TH) is $400 \mathrm{mg} / \mathrm{l}$ (as $\mathrm{CaCO}_3$ ). The amounts of $\mathrm{MgCl}_2$ and $\mathrm{CaSO}_4$ added are calculated (rounded off to the nearest integer). Which of the following options is/are true:

Atomic weights: $\mathrm{Ca}(40), \mathrm{Mg}(24), \mathrm{S}(32), \mathrm{O}(16), \mathrm{Cl}(35.5), \mathrm{C}(12)$

A
Amount of $\mathrm{MgCl}_2$ added is 143 mg
B
Amount of $\mathrm{CaSO}_4$ added is 357 mg
C
Amount of $\mathrm{MgCl}_2$ added is 103 mg
D
Amount of $\mathrm{CaSO}_4$ added is 397 mg
3
GATE CE 2024 Set 1
Numerical
+2
-0

Activated carbon is used to remove a pollutant from wastewater in a mixed batch reactor, which follows first-order reaction kinetics.

At a reaction rate of 0.38 /day, the time (in days) required to remove the pollutant by 95% is _______________ (rounded off to 1 decimal place).

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4
GATE CE 2024 Set 1
Numerical
+2
-0

A water treatment plant treats 25 MLD water with a natural alkalinity of 4.0 mg/L (as CaCO3). It is estimated that, during the coagulation of this water, 450 kg/day of calcium bicarbonate (Ca(HCO3)2) is required based on the alum dosage.

Consider the atomic weights as: Ca-40, H-1, C-12, O-16.

The quantity of pure quick lime, CaO (in kg) required for this process per day is _______ (rounded off to 2 decimal places).

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