"Henry mixed salt and water together in a cup until he observed a clear solution. He measured the mass of the solution. Then he placed the cup outside for several sunny days during the summer. After a week, he observed that only solid salt remained in the cup and the mass had decreased. Henry concluded that a physical and chemical change occurred in this investigation."Which statements correctly defend or dispute his conclusion?

A.)He is correct. Dissolving salt in water is a physical change, but evaporating the water is a chemical change. Formation of a solid is evidence that a chemical change occurred.

B.)He is correct. Evaporation is a physical change, but dissolving salt in water is a chemical change. The change in mass is evidence that a chemical change occurred.

C.)He is incorrect. Dissolving salt in water and evaporation of the water are both physical changes. The reappearance of salt is evidence that the change was reversible by a physical change, so it could not be a chemical change.

D.)He is incorrect. Dissolving salt in water and evaporation of the water are both chemical changes. The reappearance of salt is evidence that the change was reversible by a chemical change, so it could not be a physical change.

Answer:

            Empirical Formula  =  C₃H₆O₁

Solution:

Data Given:

                      Mass of Ethyl Butyrate  =  3.61 mg  =  0.00361 g

                      Mass of CO₂  =  8.22 mg  =  0.00822 g

                      Mass of H₂O  =  3.35 mg  =  0.00335 g

Step 1: Calculate %age of Elements as;

                      %C  =  (mass of CO₂ ÷ Mass of sample) × (12 ÷ 44) × 100

                      %C  =  (0.00822 ÷ 0.00361) × (12 ÷ 44) × 100

                      %C  =  (2.277) × (12 ÷ 44) × 100

                      %C  =  2.277 × 0.2727 × 100

                      %C  =  62.09 %

                      %H  =  (mass of H₂O ÷ Mass of sample) × (2.02 ÷ 18.02) × 100

                      %H  =  (0.00335 ÷ 0.00361) × (2.02 ÷ 18.02) × 100

                      %H  =  (0.9279) × (2.02 ÷ 18.02) × 100

                      %H  =  0.9279 × 0.1120 × 100

                     %H  =  10.39 %

                      %O  =  100% - (%C + %H)

                      %O  =  100% - (62.09% + 10.39%)

                      %O  =  100% - 72.48%

                      %O  =  27.52 %

Step 2: Calculate Moles of each Element;

                      Moles of C  =  %C ÷ At.Mass of C

                      Moles of C  = 62.09 ÷ 12.01

                      Moles of C  =  5.169 mol

                      Moles of H  =  %H ÷ At.Mass of H

                      Moles of H  = 10.39 ÷ 1.01

                      Moles of H  =  10.287 mol

                      Moles of O  =  %O ÷ At.Mass of O

                      Moles of O  = 27.52 ÷ 16.0

                     Moles of O  =  1.720 mol

Step 3: Find out mole ratio and simplify it;

                C                                        H                                     O

             5.169                                10.287                              1.720

       5.169/1.720                       10.287/1.720                     1.720/1.720

               3.00                                   5.98                                   1

                  3                                      ≈ 6                                     1

Result:

         Empirical Formula  =  C₃H₆O₁

Answer is (1) - atomic number.

Atomic number is unique for an element. The elements in periodic table are organized according to the atomic number of elements. Another thing is atomic number is equal to number of protons of the element.

Mass number can be defined as the sum of proton number and neutron number. Although proton number is same for the atoms of same element, the neutron number can be varied.The atoms which has same atomic number but have different number of neutrons are called isotopes. Hence, mass number not enough for the identification of elements.

Only the neutron number is also not enough for the identification of elements. But if you have both mass number and the neutron number, then you can find atomic number by using mass number = proton number + neutron number equation. Then you can identify the element.

If you have total number of electrons of the element when it is in its neutral state you can identify the element because at neutral state number of electrons = number of protons (atomic number). But if only the valence electrons are given then you cannot find the element exactly because usually all elements in certain group have same number of valence electrons.

Hello!

An antacid tablet containing 0.50 g of NaHCO3 is dissolved in 250 mL of water. What is the molar concentration of NaHCO3 in the solution ?

• We have the following data:

M (Molar Concentration or Molarity) = ? (in mol/L)

m (mass) = 0.50 g

V (volume) = 250 mL → 0.25 L

MM (Molar Mass of NaHCO3)

Na = 1*(23u) = 23 u

H = 1*(1u) = 1 u

C = 1*(12u) = 12 u

O = 3*(16u) = 48 u

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MM (Molar Mass of NaHCO3) = 23 + 1 + 12 + 48 = 84 g/mol

• We apply the data found to the formula of molar Concentration or Molarity, let's see:

Answer:  

The Molar Concentration is approximately 0.024 mol/L

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