Answer:
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Students in science class watched as their teacher demonstrated various changes. Picture A. shows a strip of magnesium ribbon, a
silver metal, in a test tube of hydrochloric acid. Bubbles are forming as the metal ribbon disappears. Also, the test tube feels warmer. Picture B. shows a container of water being heated and bubbles forming as the water bubbles. Which picture illustrates a chemical change? Explain.
A) Picture A. The magnesium ribbon disappears.
B) Picture A. Gas bubbles are produced and there is a temperature change.
C) Picture B. Bubbles are being produced as the water is being heated on the burner.
D) Picture B. There is a change in temperature as the water begins to boil and bubbles are being produced.
A) Picture A. The magnesium ribbon disappears.
B) Picture A. Gas bubbles are produced and there is a temperature change.
C) Picture B. Bubbles are being produced as the water is being heated on the burner.
D) Picture B. There is a change in temperature as the water begins to boil and bubbles are being produced.
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We have to know the molarity of solution obtained when 5.71 g of Na₂CO₃.10 H₂O is dissolved in water and made up to 250 cm³ solution.
The molarity of solution obtained when 5.71 g of sodium carbonate-10-water (Na₂CO₃.10 H₂O) is dissolved in water and made up to 250.0 cm^3 solutionis: (A) 0.08 mol dm⁻³
The molarit y of solution means the number of moles of solute present in one litre of solution. Here solute is Na₂CO₃.10 H₂O and solvent is water. Volume of solution is 250 cm³.
Molar mass of Na₂CO₃.10 H₂O is 286 grams which means mass of one mole of Na₂CO₃.10 H₂O is 286 grams.
5.71 grams of Na₂CO₃.10 H₂O is equal to = 0.0199 moles of Na₂CO₃.10 H₂O. So, 0.0199 moles of Na₂CO₃.10 H₂O present in 250 cm³ volume of solution.
Hence, number of moles of Na₂CO₃.10 H₂O present in one litre (equal to 1000 cm³) of solution is = 0.0796 moles. So, the molarity of the solution is 0.0796 mol/dm³ ≅ 0.08 mol/dm³