A sample that cannot be separated into two or more substances by physical means

Question

A sample that cannot be separated into two or more substances by physical means is a. a heterogeneous mixture. b. a compound. c. either a compound or an element. d. an element. c. a homogeneous mixture. The nucleus of a^191 Ir nuclide contains a. 191 neutrons and 268 electrons. b. 77 protons and 191 neutrons. c. 191 protons and 114 electrons. d. 191 protons, 77 neutrons, and 191 electrons, c. 77 protons and 114 neutrons. Which of the following statements concerning the limiting reactant is/are correct? 1. The mass of the limiting reactant is the always, the lowest mass of all reactant masses. 2. The theoretical yield depends on the amount of limiting reactant. 3. The moles of limiting reactant is always the lowest moles of all reactants. a. 2 only b. 3 only c. 1 and 3 d. 2 and 3 e. 1, 2, and 3 Which of the following concerning oxidation-reduction reactions is/are correct? 1. Oxidation-reduction reactions always form gaseous products. 2. At least one substance is oxidized and one substance is reduced in an oxidation-reduction reaction. 3. The species that is oxidized loses one or more electrons in an oxidation-reduction reaction. a. 1 only b. 2 only c. 3 only d. 1 and 3 e. 2 and 3

Explanation / Answer

C – Either a compound or an element.

Explanation-

A compound is a pure chemical substance made up of two or more elements in a fixed ratio by mass, which cannot be broken down into its constituent elements by physical methods. An element is already is the simplest type of matter made up of a single type of atoms. It is possible to separate both homogeneous and heterogeneous mixtures using the physical properties of the substances in the mixture.

e - 77protons and 114 neutrons

Explanation- The atomic number of 191Ir is 77 which are equal to number of protons.

Number of neutron = atomic mass – number of protons

                                    = 191 – 77 = 114

d- 2 and 3

Explanation- The limiting reactant in a chemical reaction is the substance that is totally consumed when the chemical reaction is complete, so it is the lowest moles of all the reactant. The amount of product formed (theoretical yield) is depend on limiting reactant.

e- 2 and 3

Explanation-

Reduction–oxidation reaction involves both reduction process and a complementary oxidation process. Oxidation is the loss of electrons or an increase in oxidation state by a molecule, atom, or ion.

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