Explain the difference between descriptive and injunctive norms and provide examples of each.
Descriptive norms describe what people typically do in a situation, while injunctive norms describe what is typically approved or disapproved of in a situation. Examples of descriptive norms include lining up at the checkout and quieting down at the beginning of a professor's lecture. Examples of injunctive norms include not wearing white to a wedding and the norm of reciprocity, in which people feel obligated to give back to others who have performed for them some sort of favor.
Find the Ksp for a solution of KNO3 containing .064M K+ ions at equilibrium.
The Ksp is the solubility product constant, which represents the extent to which a solute dissolves in aqueous solution. The higher the Ksp, the greater the dissolution. To solve this problem, we first write out the equation for the dissolution of KNO3 and then construct an ICE table. The equation for the dissolution is KNO3 (s) -> K+ (aq) + NO3- (aq). The Ksp expression is derived from the Kc expression, which in this case would be Kc = [K+] [NO3-] / [KNO3] The [KNO3] term refers the number of moles KNO3 in a liter of solid KNO3. Because this number does not change, we can disregard it in our calculations. Our equation for Ksp then becomes: Ksp = [K+] [NO3-] Next, we construct the ICE table. KNO3 (s) -> K+ (aq) + NO3- (aq) I ------------- 0 0 C ------------- +S +S --------------------------------------------- E ------------- S S The "I" stands for initial and represents the concentration of each product before dissolution. Since the solid has yet to dissolve, the initial concentration of both K+ (aq) and NO3- (aq) is zero. The "C" stands for change and represents the amount that each product increases to reach equilibrium concentration. Since the coefficients are the same, the products will increase equally and we can represent that number with "S". Finally, "E" stands for equilibrium and represents the concentration at equilibrium. In this case, each product has concentration S at equilibrium. Since we already know the equilibrium concentration of K+ ions is .064M and the products have the same equilibrium concentration, it follows that the equilibrium concentration of NO3- is also .064M. We can then plug those concentrations into the Ksp equation. Ksp = [K+] [NO3-] Ksp = (.064) (.064) Ksp = .0041 This indicates that the solid does not dissolve much in water.
What triggers an action potential spike and how does it occur?
Action potential spikes are governed by the opening and closing of voltage-gated ion channels, which are activated by changes in membrane potential. Non-gated K+ channels allow sodium to leak out of the cell, creating a resting potential of about -70 mV, meaning the inside of the cell is more negative than the outside. When the membrane reaches its threshold at about -55 mV, a few voltage-gated Na+ channels are opened, allowing positive ions to flow into the cell. This triggers the opening of more voltage-gated Na+ channels through positive feedback, furthering depolarization until the membrane potential becomes briefly positive and an action potential occurs. A negative potential is a restored when voltage-gated K+ channels open, allowing K+ to leave the cell, and voltage-gated Na+ channels close and remain closed. This lasts a few milliseconds and is referred to as the refractory period, during which the neuron cannot respond to further stimulation.